Fig. 3: The quantification of fibres (length and diameter) of the three commercial face masks.

The interactive fibre tracing and its correlation algorithms (skeletonizations), and thickness mapping are performed in Avizo to understand face masks microstructure, and performance. a, e, i 3D fibres are rendered as transparent (70%) with their skeletons inside. b, f, j The skeletons (curved lines) are used to track and represent each individual fibre. True fibres are deliberately masked. Skeletons are labelled to different colours (range from 50 to 750 µm, skeletons shorter than 50 µm are ignored) according to their length scale. c, g, k The corresponding length distributions of fibres are quantified. d, h, l The diameter of fibres is assigned to multiple colours that scaled is according to the fibre thickness. It should be noted that the thickness distributions are displayed above the colour bar.