Fig. 3

Biomimetic fibers with a high density of internal voids for radiative cooling. a Integrated hemispherical reflectance and emissivity spectra of a ~100-μm-thick bundle of regenerated silk fibers and a single PVDF fiber measuring ~100 μm in diameter from the visible to the mid-infrared region. Inset shows a photograph of a nanostructured PVDF fiber, a bundle of nanostructured regenerated silk fibers, and a silk thread of the comet moth. b, c SEM images of transverse and longitudinal cross-sections, respectively, of a regenerated silk fiber containing a high density of voids. d, e SEM images of transverse and longitudinal cross-sections, respectively, of a PVDF fiber containing a high density of voids