Introduction

Clothing acts as a ‘second skin’ and plays an indispensable role in thermoregulation of the human body by maintaining a comfortable microclimate against temperature shocks1,2. While traditional natural fibers have historically served this purpose, aerogel fibers (AFs), with their high porosity and ultralow thermal conductivity, and alignment with sustainable development targets, are attractive alternatives for personal thermal management3,4. However, the advancement of AFs has been persistently hindered by a fundamental trade-off between mechanical strength and thermal insulation5. An increase in porosity, which is essential for insulation, inevitably results in an exponential decay in mechanical strength, posing roadblocks to their processing via industrial weaving or knitting3,6,7. Despite extensive efforts dedicated to enhancing fiber strength from tens of kilopascals (kPa) to approximately 70 MPa8,9,10,11,12,13, this is sufficient only for manual weaving and insufficient to meet the demands of complex textile engineering.

The fabrication of AFs typically involves a solution-based spinning process, wherein the sol-gel transition is a critical determinant for AFs formation14,15. The sol-gel transition could instantaneously stabilize the nascent porous network, even within the fibrous 1D confined space, while simultaneously posing a challenge in controlling the interconnected fibril networks and across multiple length scales to effectively redistribute stress for maintaining mechanical robustness16,17. At the molecular scale, the polymer chain units are the basic determinant for the AFs' architecture. The rigid polymers with conjugated backbones, such as aramids, intrinsically contain inter- (e.g., hydrogen-bonding, π-stacking) and intramolecular (e.g., C-C, C = C) interactions to guarantee the exceptional strength ( ~ 30 GPa) and high modulus (theoretical Young’s modulus > 120 GPa), and thermal stability (limiting oxygen index >28)18,19,20,21. However, this dense, highly crystalline packing compromises moderate thermal insulation and creates significant end-of-life challenges, as the robust interactions render conventional fibers notoriously difficult to recycle22. To address these dual challenges of performance and sustainability, a transformative strategy involves deconstructing waste aramid fibers into their nanoscale building blocks, aramid nanofibers (ANFs), and reassembling them into porous aerogel architectures. This approach not only enables a circular life cycle through material upcycling but also provides a versatile platform for unprecedented structural control. The resulting high-aspect-ratio ANFs, with their rich surface chemistry, can be engineered to form an interconnected nanoporous network for underpinning stress redistribution and enabling efficient axial stress transfer19,20,21. On the mesoscale, these nanofibrils organize into a continuous nano- and micro-meter-scale porous network, which governs both thermal insulations derived from entrapped stationary air, and macroscopic force distribution by transmitting macroscopic stress along percolating fibrillar23,24,25.

The spatial arrangement of the nanofibril building blocks fundamentally determines the mechanical load-transfer pathways, whereas the porosity, pore size, and interconnectivity synergistically govern the thermal transport. This necessitates precise regulation of the building block interactions through synergistic control of the physicochemical surface properties (e.g., wetting, surface potential, and the noncovalent interaction forces)26,27,28,29 and kinetic external fields (e.g., electric/magnetic fields, solvent environment)30,31 and post-treatment processes (e.g., freeze-casting, strain alignment, and salting out)15,24,32,33,34. Whether acting on simple building blocks or the products of interfaces, microstructures, and hierarchical porous gradients, these factors facilitate the formation of a robust network and its thermal insulation performance. Despite advances in fundamental design principles, the synergistic optimization of mechanical strength and thermal insulation in AFs, while simultaneously enabling scalable production, remains an open issue.

Herein, we present and validate a strategy for tuning the hierarchical structures of AFs using recyclable heterocyclic aramid nanofibers (HANFs) as nanobuilding blocks. This strategy is compatible with industrial wet-spinning, enabling the fabrication of fibers with remarkable mechanical strength by controlling building blocks' hierarchical assembly, which synergistically combines molecular engineering with charge modulation to coordinate surface potential and coacervation kinetics. The resulting hierarchical HANF-AF achieves both the desired thermal insulation (22.0 mW·m-1·K-1) and robust mechanical properties (tensile strength 83.1 MPa). Thermoregulatory textiles have been manufactured via a commercial automated knitting process to verify their industrial processability. The resulting knitted fabric provides a 5.1 °C greater temperature difference than does its cotton counterpart. This work establishes a scalable and sustainable pathway that bridges molecular-level design with industrial manufacturing, accelerating the translation of high-performance thermally insulating fibers from laboratory innovations to market-ready applications.

Results

Fabrication of hierarchical HANF-AF and textile engineering

Figure 1a and Supplementary Movie 1 illustrate the wet-spinning process for hierarchical HANF-AF production, which encompasses extrusion, coagulation, washing/drafting, solvent exchange, and supercritical drying conducted on a custom-built wet-spinning line. During the coagulation stage, the recyclable nanobuilding blocks of HANFs assemble into a hierarchical structure involving both a secondary assembly, including proton-mediated nanofibers assembly and nonsolvent-induced phase separation (NIPS) (Fig. 1b). As summarized in Fig. 1c, the resulting HANF-AF demonstrates a superior combination of mechanical-porosity compared with state-of-the-art counterparts (Kevlar-ANF, polyimide, and biomass) (Supplementary Data 1). They could achieve an unprecedentedly broad tunable range of tensile strengths of 30.4-133.1 MPa within a porosity range of 59.8-95.4%, through coagulation bath and drafting ratio regulation (Supplementary Fig. 10 and Table 1).

Fig. 1: Tunable fabrication of hierarchical HANF-AFs and textile engineering.
Fig. 1: Tunable fabrication of hierarchical HANF-AFs and textile engineering.The alternative text for this image may have been generated using AI.
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a Hierarchical HANF-AF fabrication via a wet-spinning process. b Schematic of proton-mediated phase-inversion in the wet-spinning sol-gel transition, illustrating hierarchical assembly via surface charge modulation and dual-diffusion. c Ashby diagrams of ultimate porosity versus ultimate tensile strain. d Photograph of HANF-AF tows demonstrating scalable manufacturing. e Industrial knitting of a thermoregulatory garment from HANF-AF. f The HANF-AF fabric (left) was produced on an automatic knitting machine, with magnified views showing the regular knit textile structure (right, top) and the flexibility of the folded fabric (right, bottom). g The knitted vests made from HANF-AF fabric (left) and cotton fabric (right), and (h) corresponding infrared thermal images tested in an 0 °C environment chamber.

To validate the scalability, we established a liter-scale HANF dope preparation facility to match kilogram-level HANF-AF production via continuous 50×, 100×, and 200×filament wet-spinning (Supplementary Figs. 8 and 9 and 11). The resulting 50-filament yarn (Fig. 1d) exhibited exceptional flexibility and robustness, characterized by a tensile strength of 2.0 cN/dtex, a maximum breaking load of 12.4 N, an elongation at break of 16.2%, and an elastic modulus of 33.1 cN/dtex, while maintaining a single-fiber porosity of 84.3% and tensile strength of 84.7 MPa (Supplementary Fig. 12). This desirable flexibility and mechanical robustness guarantee yarn processability on commercial automated knitting machines, where yarns are successfully knitted into large-area fabrics, ultimately sewn into a vest for further thermal insulation evaluation (Fig. 1f, g). The resulting thermal vest provides a 5.4 °C temperature gradient compared with its cotton counterpart (Fig. 1h) at 0 °C environmental temperature.

Recycling engineering of 3.4 nm HANF from waste aramid fibers

The top-down recycling strategy establishes a circular life cycle for aramid fiber by upcycling industrial waste and post-consumer materials into functional nanoscale building blocks, thereby addressing critical challenges in resource efficiency, waste management, and polymer recovery35,36. As illustrated in Fig. 2a and Supplementary Fig. 13a, this closed-loop paradigm enables the direct regeneration of HANF spinning dopes from waste aramid resources and post-consumer aerogel textiles. These HANFs are subsequently harnessed to wet-spin into HANF-AF and knit into a useful textile. This approach delivers a sustainable and scalable strategy for manufacturing high-performance thermal insulation materials, which bridge the gap between sustainable polymer reprocessing and next-generation functional textiles development.

Fig. 2: Sustainable fabrication and characterization of ultrafine HANFs.
Fig. 2: Sustainable fabrication and characterization of ultrafine HANFs.The alternative text for this image may have been generated using AI.
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a Recycling protocol for waste aramids fibers and aerogel fiber production workflow. b Multiscale structural hierarchy of aramid fibers. The KOH/DMSO superbase organic solvent system effectively disrupts interchain H-bonds, leading to stable dispersions of nanofibers with high electronegativity and electrostatic repulsion. c Atomic force microscopy (AFM) image of the resulting HANFs. d Frequency distribution of the width for individual HANFs and Kevlar-ANFs. The width for Kevlar-ANFs is representative of found in the literature37.

The exfoliation process is initiated by the anisotropic swelling of heterocyclic aramid microfibers upon immersion in the KOH/ dimethyl sulfoxide (DMSO) superbase system (Fig. 2b), which causes their diameter to expand from 14.1 μm to over 25.0 μm while retaining the nematic liquid-crystalline texture and progressively disintegrating into micrometer-scale fibril aggregates (Supplementary Figs. 6 and 7). This structural breakdown driven at the molecular level by the infiltration of DMSO and hydroxide ions35, which disrupt the dense intermolecular H-bonding network, yields a complete dispersion of individual, negatively charged HANFs (Supplementary Fig. 3). Notably, the unique molecular architecture of the heterocyclic aramid of the N-H bond dissociation energy of the benzimidazole group (82.4 kcal mol-1) is significantly lower than that of the amide group (91.4 kcal mol-1), rendering it more susceptible to deprotonation by the superbase (Supplementary Figs. 1 and 3). The as-prepared HANFs demonstrated an ultrafine morphology with an average width of 3.4 ± 0.9 nm (Fig. 2c, d, and Supplementary Fig. 14). This dimension is substantially finer than that of conventionally produced Kevlar aramid nanofibers (ANFs) (18.4 ± 5.5 nm)37 and approaches the width of a single heterocyclic aramid (Poly (p-phenylene-benzimidazole-terephthalamide, PBIA) molecular chain (0.5 ± 0.2 nm).

HANF secondary assembly

The intrinsic features of the nanobuilding blocks, coupled with the characteristics of the junction between them (e.g., entanglements, H-bonds), are the determinants of the mechanical and thermal-insulating performance of the final HANF-AF. As schematically illustrated in Fig. 3a, the dimensional variations among the PBIA polymer chains, HANF and Kevlar-ANF exhibited a significant size effect on the assembly process (Supplementary Figs. 15 and 16). The ultrafine HANFs not only provide abundant active interfaces for network formation, but also establish a versatile material platform for precise structural engineering across nano-, micro-, and macroscopic scales38.

Fig. 3: Basic principles of HANF secondary assembly.
Fig. 3: Basic principles of HANF secondary assembly.The alternative text for this image may have been generated using AI.
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a Schematic illustrating the correlation between fiber porosity and strength for different nanobuilding block widths. b Schematic illustration of proton-induced nanofiber structural evolution and interfibrillar interactions during HANF attenuated Coulombic self-assembly. The number of ↑ means the magnitude of non-covalent interaction forces received during the HANF phase separation process. c Zeta potential of HANF dispersions under titration with various acid concentrations. pH~11.5 is the critical point for attenuated Coulombic behaviour in HANFs. Data are presented as mean ± s.d. of n  =  3 independent experiments. d UV-vis spectra of HANF dispersions under titration with varying acid concentrations. UV-vis, ultraviolet-visible light. e Ternary phase diagram of HANF/DMSO/acid aqueous systems, with blue-yellow gradient areas reflecting the trend of increasing demand for non-solvent content during the phase separation process. f Photographs showing changes in color and viscosity upon the addition of 1.0 wt% acid. g Snapshots from CG-MD simulations showing the structural evolution of charged nanofibers with varying degrees of protonation (For visualization of assembly structures, both yellow and green beads represent coarse-grained HANF chains, with green beads highlighting 100 chains and yellow beads representing the remainder).

HANF assembly is dictated by a balance between noncovalent interactions (H-bonding, π-π stacking, van der Waals) and electrostatic repulsion, both of which originate from the charged states of the amide and imidazole groups (Supplementary Figs. 3 and 20). These groups exhibit distinct protonation kinetics37,39,40, enabling the programmed stepwise assembly. As illustrated in Fig. 3b the formation of complex hierarchical structures arises from HANF assembly, which is governed by proton-triggered synergistic Coulombic attenuating forces and noncovalent interactions, proceeding via a two-stage pathway. First, ultrafine nanofibers coalesce laterally to form nanofibril bundles. Subsequently, these nascent nanobundles undergo further micellar condensation, progressively maturing into assemblies. The Coulombic interactions, quantified by the Zeta potential (ζ), govern the separated distances26. Within the KOH/DMSO superbase system, HANFs achieve exceptional electrostatic stabilization via strong negatively charged inter-fibril repulsion (ζ = −46.1 mV). The introduction of an acidic coagulant dramatically modulates these interactions. As the proton (H⁺) concentration increases, the negative surface charge on HANF is progressively neutralized (Supplementary Fig. 17). As depicted in Fig. 3c, this process leads to significant Zeta potential reduction with a critical point of pH~11.5 (ζ = −14.3 mV), which attenuates the repulsive Coulombic barrier, thereby initiating the bundling of HANFs.

In particular, proton introduction-triggered H-bonding reconstruction is attributed to the preferential protonation of high-pKa amide groups over imidazole groups, as spectroscopically evidenced by the progressive intensification of the amide II (1537 cm-1) and amide I (1658 cm-1) bands depicted in the FT-IR spectra (Supplementary Fig. 18b and c). The increase in the characteristic peak at 1257 cm-1, assigned to the imidazole N-H bond, subsequently signals the onset of the second protonation stage, which drives the coalescence of nanofibrils (Supplementary Fig. 18d). This two-stage transition upon protonation was further corroborated by UV-vis spectroscopy, which revealed a progressive blueshift of the absorption peak from 420 nm (deprotonated state) to 360 nm (aggregated state) (Fig. 3d and Supplementary Fig. 19).

The protonation of charged amide/imidazole groups (H⁺ + -N⁻- → -NH-) is an exothermic process driven by a favorable enthalpy change. Concurrently, a multitude of noncovalent interactions (Supplementary Fig. 19) push the neutralized nanofibers into interfacial regions, facilitating the formation of aggregate structures. Linearized Cloud Point (LCP)41 calculations and the experimental phase diagram (Supplementary Figs. 21 and 22) confirm that the proton-triggered assembly of HANF is an effective excess enthalpy process. This acid-accelerated phase separation is explicitly summarized in the HANF-DMSO-H2O ternary phase diagram (Fig. 3e). As the acidity increases, the binodal curve, defined by the cloud-point, shifts towards the HANF-DMSO binary axis, reflecting the reduced nonsolvent or equivalently, an elevated nanofiber concentration required to initiate phase separation. For example, in a 2 wt% HANF dispersion, acidification of nonsolvent reduces the phase separation threshold from 30 vol% (pure water) to 16 vol% (2 wt% aqueous acid solution), demonstrating the critical role of acidity in modulating the thermodynamic boundaries of phase separation.

The acid-triggered microstructural evolution of HANF aggregates further drives significant macroscopic rheological transitions. As shown in Fig. 3f and Supplementary Fig. 23, the zero-shear viscosity surges from 3.4 Pa·s to 29.5 Pa·s (8.4-fold increase) at the critical gelation threshold (0.5 wt% acid), indicating progressive an inter-nanofiber crosslinking and percolating network. To bridge the molecular-level interactions with this multi-scale assembly, and to visualize the underlying assembly dynamics, we performed coarse-grained molecular dynamics (CG-MD) simulations. In simulations modeling the experimental protonation assembly, we progressively reduced the negative charge on nanofiber beads, directly mimicking the attenuation of electrostatic repulsion (quantified by Zeta potential as high, moderate, and low, Fig. 3g). These simulations provide compelling visual confirmation of gelation (Fig. 3g and Supplementary Figs. 24–27), revealing that reduced Coulombic repulsion triggers nanofibers coalescence into denser aggregates (driven by short-range attractions) while expanding inter-aggregate voids. This simulated aggregation provides a direct mesoscopic snapshot that connects the molecular-level H-bond reconstruction (FT-IR) and electronic transitions (UV-vis) to the macroscopic thermodynamic changes (phase diagram, Fig. 3d and e) and gelation (rheology, Fig. 3f). Collectively, spectroscopy, zeta potential, phase mapping, rheology, and CG-MD simulations form a cohesive, multi-scale framework. This demonstrates that modulating electrostatic barriers through protonation kinetics deterministically controls coagulation dynamics and hierarchical pore architecture, enabling precise microstructural engineering of HANF-AFs. Collectively, these results demonstrate that modulating electrostatic barriers via protonation kinetics deterministically controls coagulation dynamics and hierarchical pore architecture, thereby enabling microstructural engineering of HANF-AF.

HANF-AF hierarchical architectures and thermal-mechanical performance

To elucidate the dynamic phase evolution and hierarchical architecture formation within the one-dimensional confinement of a spinning filament, we employed in-situ polarized optical microscopy (POM) coupled with high-speed imaging (Supplementary Fig. 28). As depicted in Fig. 4a, the NIPS initiates at the extrudate surface, where steep coagulant/solvent concentration gradients drive rapid solidification, forming a continuous semi-permeable skin layer. Time-resolved POM images show birefringent gelation fronts propagating radially inward from this skin layer toward the isotropic core as the structure develops and matures. In addition, the solidification front propagation speed is proportional to acid concentration in the coagulation bath (Supplementary Figs. 29 and 30). As summarized in Fig. 4b, the extrusion filament gelation rate in a 10 wt% acid coagulation bath is 1.8 times faster than that in a 2 wt% acid bath.

Fig. 4: Microstructure of HANF-AFs and their thermal/mechanical properties.
Fig. 4: Microstructure of HANF-AFs and their thermal/mechanical properties.The alternative text for this image may have been generated using AI.
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a Bright-field and polarized microscopy images, captured in-situ of wet-spinning nascent fiber, reveal the evolving gel morphology and liquid crystal orientation during the formation process. b Gelation front of boundary position displacement versus time profile. Data are presented as mean ± s.d. of n  =  3 independent experiments. c Hierarchically porous structure of a fiber in a 2 wt% H2SO4 coagulation bath. d Representative stress-strain curves comparing AF: isotropic Kevlar-ANF, isotropic HANF (see Supplementary Fig. 10 A-II), hierarchical HANF (2 wt% H2SO4 coagulation bath), and hierarchical HANF with a draft ratio of 1.7. e, f Uniaxial tensile simulations elucidating the underlying strengthening mechanisms. Snapshots display the Mises stress distribution for four representative nanofiber network models, viewed from the (e) top and (f) front. g Schematic illustration of the thermal conductivity of aerogel fibers with hierarchical pore structures and isotropic three-dimensional network structures. h Temperature difference (ΔT) between the fiber surface and the hot substrate versus a 1-layer aerogel fiber. i Ashby diagrams of ultimate thermal conductivity versus ultimate tensile strain.

The porous architecture of HANF-AFn (n denotes acid identity/concentration) is engineered through a synergistic interplay of thermodynamic/kinetic control (Supplementary Figs. 31-33) and mechanical drafting, with bath acidity acting as a variable governing nanofibril bundling and hierarchical assembly (Supplementary Figs. 34 and 35). Modulating coagulation bath acidity serves as a key control parameter, where the introduction of protons suppresses elastocapillary thinning and internal stress of the aggregate network through attenuating the electrostatic repulsion rate (Supplementary Fig. 36)42, yielding expanded fiber diameters and elevated elaborate porosity (Supplementary Fig. 40). Fundamentally, this high performance is rooted in the selection of heterocyclic aramid nanofibers (HANFs), which proved to be a superior nanobuilding block compared to conventional Kevlar- and meta-aramid nanofibers for achieving both high strength and high porosity (Supplementary Fig. 39 and Note 2). This transition increases the total porosity from 56.3% (HANF-AFH₂O) to 95.4% (HANF-AF20wt%H₂SO₄, Supplementary Fig. 36c). As depicted in Fig. 4c, HANF-AF2wt%H₂SO₄ exhibited a radially skin-shell-core graded porous architecture, where each hierarchical layer presented distinct mechanical and thermal features. This architecture contains gradient macropores (0.5–5 μm) within the shell layer and a fine nanoporous structure (3–50 nm) that constitutes the solid matrix of both the macropore walls and the core layer, as confirmed by mercury intrusion porosimetry (Supplementary Figs. 38, 40–43).

Fracture failure analysis (SEM images in Supplementary Fig. 45) reveals fibril pull-out toughening in core and skin regions, where protruding the intrinsic high strength of nanofibrils43. In-situ compression and nanoindentation (Supplementary Figs. 46 and 47) validate enhanced load-transfer efficiency in the core microstructure. As a result, HANF-AF achieves a superior strength-porosity balancing feature (Fig. 1c and Supplementary Figs. 10 and 48, detailed parameters in Supplementary Data 2 and Supplementary Table 3), which is attributed to the uniform hierarchically porous structure and synergistic dense-packed aligned structure with a continuous uniform nanoporous core structure. In addition, the drafting also enables microstructural alignment, which confers substantial mechanical reinforcement. The drafted AF2wt%H₂SO₄ mixture achieves a tensile strength of 111.2 MPa, representing a 271% enhancement over its undrawn counterparts (30.4 MPa, Fig. 4d and Supplementary Figs. 49 and 50, and Table 1). Beyond these impressive static properties, the fibers exhibit excellent dynamic performance critical for textile applications. They demonstrate outstanding fatigue resistance, robustly withstanding 5000 cycles of both severe 180° bending and high-stress tensile loading with negligible degradation (Supplementary Fig. 51).

To elucidate the reinforcement mechanisms by hierarchical architecture and nanofiber orientation, we perform a simulation to analyze non-covalent forces (e.g., slippage, pull-out) during the fracture process with 3D Timoshenko beam-element chains representing individual nanofibers (Supplementary Figs. 52–54). Three architecturally distinct models with the assigned consistent porosity and density have been built with the characteristics of isotropic network, aligned network, and aligned-hierarchical network, respectively (Fig. 4e). Progressive microstructural reorganization, such as nanofiber straightening, reorientation, and pore compression, gradually emerged accompanied by the sequential deformation (Supplementary Fig. 55). As depicted in Fig. 4f, at 20% tensile strain, the ‘aligned-hierarchical’ fiber demonstrated uniform force distribution with enhanced stress transfer efficiency between nanofibers compared with ‘isotropic’ and only ‘aligned’ counterparts. Critically, the hierarchical architecture facilitated macropore-wall densification, increasing load-bearing capability (Supplementary Fig. 56). Thus, synergistic contributions from enhanced interfibrillar interactions, optimized nanofiber orientation, and hierarchical structural assembly collectively govern the macroscopic tensile performance.

The exceptional thermal insulation of HANF-AFs originates from their precisely engineered hierarchical porosity (Fig. 4g), which traps stationary air with closed macropores (2 μm) and nanopores (sub-50 nm)23. Crucially, the fine and dense nanopores have dimensions smaller than the mean free path of air molecules ( ~ 70 nm)25, inducing a Knudsen diffusion regime that suppresses gaseous conduction and convection. Concurrently, the macro-porous cellular shell compartmentalizes air into semi-enclosed cells, thereby suppressing large-scale convective loops. Furthermore, solid-phase thermal conduction is minimized through interfacial phonon scattering within the ultrafine (3.4 nm) nanofibrillar network and the elongation of heat-transfer pathways. The hierarchical architecture also functions as an intrinsic and efficient radiation barrier, effectively attenuating thermal radiation (Supplementary Fig. 60)3,44,45,46. Therefore, this exceptional insulating performance arises not from a single mechanism but from the synergistic suppression of all four heat transfer modes—gas conduction, solid conduction, convection, and radiation—enabled by the hierarchical design. This integrated approach achieves a remarkably low thermal conductivity of 22.0 mW·m-1·K-1 with a porosity of 89.1%. Infrared thermography confirmed superior thermal resistance (Fig. 4h and Supplementary Figs. 57 and 58) that a single-layer HANF-AF mat (120 μm) achieved 5.9 μm/K on a 100 °C substrate, outperforming for Kevlar-ANF-AF (9.9 μm/K), despite a larger fiber diameter (180 μm) and higher porosity (96.7%) (Supplementary Figs. 39f and 59). Figure 4i further highlights the exceptional thermomechanical performance of HANF-AFs, exhibiting a thermal conductivity of 22.0–65.5 mW·m-1·K-1 and tensile strength of 30.4-133.1 MPa, surpassing traditional thermal-insulating fibers (SiO2, cellulose, silk) and synthetic aerogel fibers (PBO, polyimide) (Supplementary Table 1 and Supplementary Data 1).

Wearable textile engineering and multifunctional thermal management

The successful industrial-scale knitting of HANF-AF represents a critical milestone towards personal thermal management, as conventional aerogels typically suffer from fragility and poor bendability, which can cause catastrophic fracture during yarn, textile and fabric preparation. As demonstrated in Fig. 5a, the current HANF-AF yarn enables continuous processing of commercial flat knitting machinery without mechanical failure. The batch-produced HANF-AF yarn (containing 50-filaments) exhibited a breaking load exceeding 12 N (Supplementary Fig. 12), substantially surpassing the ~3.4 N threshold required for industrial knitting machinery. A series of joint vests with splicing a HANF-AF fabric (left) and a counterpart fabric (right) have been fabricated directly from yarn via a programmed knitting process (Supplementary Figs. 61 and 62, and Movie 2). The knitted HANF-AF textile exhibited a uniform and smooth texture (Fig. 5b) and with excellent mechanical flexibility, was capable of withstand extreme deformation, such as 180° twisting and folding (Supplementary Fig. 63). The float-plated HANF-AF fabric with a minimal thickness of 0.82 mm, exhibits a thermal conductivity of 43.5 ± 1.2 mW·m-1·K-1, which is significantly inferior to polyimide (75.1 mW·m-1·K-1), aramid (64.3 mW·m-1·K-1), silk (72.7 mW·m-1·K-1), cotton (66.3 mW·m-1·K-1), and polyester (93.7 mW·m-1·K-1) (Supplementary Figs. 64–66 and Table 2 and Movie 3). This value is higher than that of a single fiber, primarily due to convective heat transfer within the fabric’s macroscopic pores47. Nevertheless, the knitted architecture was deliberately selected for its unique advantages in wearable thermal management. The interlooping structure provides critical flexibility and resilience, while simultaneously trapping a substantial layer of static air to enhance the overall breathable and insulation performance of the garment48.

Fig. 5: The knitted HANF-AF fabric with outstanding thermal insulating ability.
Fig. 5: The knitted HANF-AF fabric with outstanding thermal insulating ability.The alternative text for this image may have been generated using AI.
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a Designing the fabric structure and vest patterns, industrial knitting fabric, integrating fabric pieces, and sewing zippers for HANF-AF-based vests, indicating the potential of large-scale production. b Mechanical resilience and flexibility of the knitted HANF-AF fabric. c Thermal manikin dressed in a vest made of HANF-AF fabric (left) and cotton fabric (right), with surface temperature measurements taken after 30 s and 20 min in a 0 °C environmental chamber. d Photograph of a vest made of HANF-AF (left), aramid, silk, and polyester fabrics, and the corresponding infrared thermal images. e Fabric surface temperature tracking for HANF-AF and cotton. The curves represent the mean surface temperatures, as exemplified by the white dotted box in Fig. 5c. f Experimental setup for outdoor garment thermal performance testing in Beijing, China (40°4′22″N, 116°10′19″E, January 21, 2025, 23:20 Beijing time, outdoor temperature ~ −2.2 °C). g Thermal images of a volunteer wearing a custom-made vest (HANF-AF fabric and cotton fabric). h Curves of the surface temperatures of the HANF-AF fabric and cotton fabric.

Afterwards, as displayed in Fig. 5c, the joint vest thermal management performance was evaluated using a thermal manikin system in a 0 °C environmental chamber. The HANF-AF side demonstrated superior insulation performance, characterized by maintaining a higher manikin skin temperature (32.7 °C for HANF-AF vs. 31.3 °C for cotton). As depicted in the infrared thermography of Fig. 5c and the summary curve in Fig. 5e, the HANF-AF fabric (0.037 g cm-2 areal density) exhibited a spatial thermal uniformity with stabilized outer surface temperatures averaging 11.1 °C, maintaining a large temperature gradient of 21.6 °C relative to the manikin skin, even after maintaining 20 min (Supplementary Movie 4). This represents a 5.1°C greater temperature difference than that of cotton fabric under consistent conditions. The infrared thermograph in Fig. 5d further proved that the conventional aramid, silk, and polyester fabrics depicted inferior thermal insulation properties with stable outer surface temperatures of 18.8, 18.3, and 19.4 °C, respectively, even with a higher areal density of 0.059-0.065 g cm-2 (Supplementary Table 2).

To validate the thermal insulation capability of the HANF-AF fabric, field testing was performed under real winter conditions (−2.2 °C, 3.0 km/h, gentle breeze, zero solar irradiation). A volunteer wore the splicing thermal vest, comprising HANF-AF fabric and cotton fabric on the counter side (Fig. 5f and Supplementary Fig. 68 and Movie 5). Time-resolved infrared thermography revealed a distinct delay in thermal equilibration for the HANF-AF side (80.7 s) compared to cotton (45.5 s). At steady state, the HANF-AF exterior surface maintained a 3.1 °C lower temperature than cotton, confirming reduced thermal dissipation. Upon removing the vest, the infrared analysis further revealed >1.7 °C higher skin temperature beneath the HANF-AF section versus the cotton-covered range. The HANF-AF fabric exhibits exceptional thermal durability, maintaining over 97% of its original insulating capability after undergoing repeated thermal cycling between 100 °C and −196 °C (Supplementary Fig. 70). This resilience highlights its reliability for applications subject to extreme and dynamic temperature fluctuations. Furthermore, after encapsulation of HANF-AF within thermoplastic polyurethane (TPU), stable water repellency and thermal insulation were achieved (Supplementary Figs. 69, 71, and 72), establishing a foundation for next-generation machine-washable thermal insulating textiles.

Discussion

We have developed a kinetically controlled, acid-triggered assembly strategy to fabricate hierarchical aramid nanofiber aerogel fibers that overcome the classic trade-off between thermal insulation and mechanical robustness. Multiscale characterization of the fiber and simulations confirmed that this hierarchical structure is also the source of the fiber's low thermal conductivity and textile processability. The successful fabrication of these fibers from recycled sources into functional garments via industrial processes highlights a viable pathway toward sustainable, high-performance textiles. This work provides a scalable, sustainable route to translate the exceptional properties of aerogels into fiber-based materials for wearable thermal management.

Methods

Chemicals and resources

The waste heterocyclic aramid fibers were procured from China Bluestar Chengrand Co., Ltd. Dimethylsulfoxide (DMSO, 99.7%), Na2CO3, and KOH were purchased from the Aladdin Chemical Reagent Co., Ltd. (Shanghai, China). Ethanol ( > 99.5%), tert-butanol, hydrochloric acid, sulfuric acid, acetic acid, and phosphoric acid were all obtained from Adams-beta Co., Ltd (Shanghai, China). Deionized water was produced using a Millipore water purification system.

Preparation of HANF spinning dopes

To prepare the nanofiber spinning dope, waste aramid fibers are washed, chopped, pre-dissolution in a superbase (DMSO/KOH) solvent system, stirred, and filtration. Initially, waste aramid fibers were boiled in 0.2 M Na2CO3 solution for 30 minutes, followed by washing with purified water three times. Subsequently, the dried, chopped aramid fibers (0.5-1.0 cm) were added to 2 L of dimethyl sulfoxide (DMSO) containing 1.5 wt% KOH and 2.0 wt% water. This mixture underwent 24 h of pre-dissolution and 24 h of magnetic stirring at room temperature, yielding a dark red, viscous dispersion of heterocyclic aramid nanofibers (HANF). Finally, the dark red dispersion was filtered to obtain the homogeneous spinning dopes. These dopes remained stable, exhibiting no agglomeration and flocculation, attributed to the deprotonation and electrostatic repulsion between the nanofibers.

Preparation of HANF-AF

HANF-AFs were prepared via a wet-spinning process. A 2 wt% HANF spinning dope was extruded into an aqueous acid coagulation bath. Upon coagulation, indicated by a color transition of the nascent filaments from dark brown to pale yellow, the filaments were washed, draft in a secondary bath, and wound as hydrogel fibers. The resulting hydrogel fibers were first aged in deionized water to remove residual acid and DMSO, followed by immersion in a 25 wt% aqueous tert-butanol solution for 12 h. Finally, the hydrogel fibers were frozen in liquid nitrogen and lyophilized at −44.5 °C and 0.120 mbar (Labconco) to produce the final aerogel fibers. Unless otherwise specified, all characterizations were performed on these freeze-dried samples.

For scalable fabrication, multifilament and weavable yarns were prepared via a supercritical drying process. Key spinning parameters included a spinneret with 50 holes (Φ0.25 mm each), a coagulation bath of 2 wt% H2SO4 aqueous, and a draft ratio of 1.3. The collected hydrogel fibers were subjected to three solvent exchange cycles in anhydrous ethanol before being supercritically dried at 35 °C and 9.5 MPa for 12 h.

Characterization and measurement

Chemical structures were recorded using a Fourier-transform infrared (FTIR) spectrometer (Thermo Scientific, Germany) and a Raman spectrum (LabRAM Odyssey, Horiba) with a 633nm laser excitation. Nanofiber surface morphology was measured by atomic force microscopy (AFM, Dimension ICON, Bruker, Germany). Samples for AFM were prepared by depositing a 5 μL droplet of an ultra-dilute HANF suspension (0.00005 wt% in ethanol) onto a freshly cleaved silicon wafer (1 × 1 cm), followed by air drying. The zeta potential of diluted HANF dispersions was measured using a Zetasizer (Malvern, UK). The measurements were performed on HANF dispersions diluted to 1.0 mg/mL in a DMSO solution to ensure accurate readings. Optical properties, including the transmittance for cloud point determination and UV-vis absorption spectra, were recorded on a UV-VIS-NIR spectrometer (Perkin Elmer Lambda 950, America). For titration experiments, a 0.125 wt% HANF dispersion was used, and the acidic titrant was pre-diluted in DMSO to prevent rapid, localized aggregation. The residual DMSO content in aqueous solutions was quantified by high-performance liquid chromatography-mass spectrometry (HPLC-MS, LC-30AD-8050 MS, Japan). Rheological properties of the spinning dopes were characterized over a shear rate range of 0.1 to 1000 s-1 using a rheometer (TA Instruments DHR-2, American) with a parallel-plate geometry. The in-situ dynamics of double diffusion and the formation of liquid crystalline structures in precursor HANF fibers under acidic coagulation bath were recorded using an optical microscope (Nikon Eclipse) equipped with a high-speed camera (AMETEK, MIRO C321, American) operating at 200-2000 fps.

The cross-section morphology and porous nanoscale architecture of the fibers were examined using field-emission scanning electron microscopy (FESEM, Regulus8220, JEOL, Japan) at an accelerating voltage of 10 kV. Structural characterization at the nanoscale was performed at the Shanghai Synchrotron Radiation Facility, where wide-angle X-ray diffraction (WAXD) patterns were collected. Mechanical properties of single filaments were assessed using a universal testing machine (CMT6103) equipped with a 5 N load sensor. The specific surface area and pore size distribution of the aerogel fibers were determined by N2 adsorption-desorption isotherms using a Brunauer-Emmett-Teller (BET) analyzer (ASAP 2020, USA) and mercury intrusion porosimetry (Autopore IV 9500, USA). Tensile tests of single fibers were conducted with a 1 cm gauge length at a strain rate of 1 mm/min, and all reported values represent the average of at least seven independent measurements. Mechanical strength of the aerogel fibers yarn was evaluated using an MTS Exceed Model E43 machine with yarns of 62 T/m twist and 17 cm length. Indentation experiments were conducted along the fiber axis at a constant loading rate of 0.08 μm/s in a custom-made in situ nanomechanical instrument (SEMentor) with a 5-μm-diameter flat conical diamond indenter tip.

To measure the thermal conductivity of the HANF-AF, we prepared a HANF foam with a similar aligned porous structure for estimation. The thermal conductivity (λ) of the fabrics was measured using the transient plane source method with a thermal constant analyzer (TPS 2500 S, Hot Disk, Sweden) under heating power of 5 mW and heating time of 10 s. In detail, the Kapton probe (type 7281) was placed in the middle of two pieces of fabric, and a certain pressure was applied above the fabric, followed by stabilization for 60 min to start the test. Thermal imaging and temperature mapping were performed using a high-resolution thermal camera (FLIR Systems Inc., A700, America).

Fabrication of knitted textiles

The interlooping architecture of knitted fabrics imparts inherent extensibility and three-dimensional conformability, which can effectively mitigate mechanical damage to brittle aerogel fibers and enhance the volume of the entrapped static air layer, thereby improving thermal insulation. However, high-speed knitting imposes significant stress on yarns as they pass through tensioners, feeders, and are rapidly formed into loops by needles, often leading to catastrophic fiber failure. Such failures result in processing interruptions and critical fabric defects, including uneven loop sizes, dropped stitches, and holes. Our batch produced aerogel fiber yarn, exhibiting a breaking load exceeding 12.0 N, comfortably met the tensile requirements for low-speed operation of the commercial flat knitting machine (Stoll CMS 530, 7.2-gauge), which operates at 3.4–5.0 N. To visualize the knitting process and details of the HANF-AF yarn, clear footage of the knitting procedure was captured using a flat knitting machine (SWG061N2, Shimajima Seiki Co., Ltd., Kochi).

The overall process involved: establishing the knitted fabric structure, designing the garment pattern, inputting and applying knitted machine design parameters, fabricating the knitted fabric swatches, and integrating zipper closures at the shoulder, side waist, and center front locations (Fig. 5a). A vest garment was designed and fabricated for adult males with a height of 180 cm. To minimize stress on the yarn, a float-plated fleecy stitch structure was selected, wherein the aerogel fibers served as the fleecy yarn and a commercial aramid fiber was used as the ground yarn. For consistent comparison, control fabrics made from silk, cotton, aramid, and polyester yarns were also prepared with the same knitted structure. Finally, the resulting fabric swatches were integrated via zipper stitching to produce a bipartite insulated vest for thermal performance evaluation.

Warm manikin system test

The thermal insulation performance of the fabrics was evaluated using a thermal manikin system (Thermetrics, America). All tests were conducted within a climatic chamber maintained at 0 °C to simulate a cold environment. The manikin, featuring multiple independently heated zones to ensure a uniform surface temperature, was maintained at a constant 35.0 °C. For each test, the manikin was first outfitted with a standard base layer of clothing (trousers, socks, shoes, and a hat) before the insulated vest was donned. The entire assembly was allowed to reach thermal steady state, at which point a thermal camera recorded the temperature distribution across the vest’s outer surface.

On-body thermal-insulation test

To validate the heat-retention capability of the HANF-AF fabric in a practical setting, a field test was conducted under cold winter conditions in Beijing, China. The ambient environment was maintained at −2 °C, with a gentle breeze of approximately 3km/h and no solar irradiation. A volunteer wore the custom-fabricated bipartite vest, and the evolution of the external surface temperatures was monitored using a thermal camera. As the study protocol was non-invasive, ethics oversight was waived. The research participant provided signed informed consent to participate in the study and to have their images and movies published.