## 3 Results and Discussion  
Figure 1a shows the arrangement for the pressure and velocity measurements made in the manner described above. The air duct was designed and sealed around the mask, positioned transversely at its centre (mask gasket sealed within the chamber). Pitot tubes, central to the air flow, were positioned at 7.5 cm on either side (see inset Figure 1b). In order to prevent leakage, each mask layer was sealed with a clamped rectangular gasket rim. Figure 2a-f show SEM micrographs displaying porosity in both woven and random fiber structures. Pores lie between the cross weave and within overlaying fibers with random orientations. Figure 2a,c,d are randomly orientated fibers, and Figure 2b,e,f are woven or ordered fabrics. The average pore sizes vary within the different mask layers, as indicated in Table 1. Further structural details have been reported earlier by [PERSON] et al. (2022) [36]. Figure 2g,h show the relative pore size and fiber diameter of the mask's constituents based upon SEM measurements. Each SEM image shows the texture as an ordered weave or random overlay of fine fibers, revealing porosity and fiber diameter. Clearly, _Reusable Cotton_ has the largest and _FFP3_ has the lowest pore size, whereas _Antiviral_ with _Silk_, and _Surgical_ with _FFP2_ showed comparable pore sizes. Fiber diameters lay in a narrow range, with the largest and smallest applying to _Surgical_ and _Silk_, respectively [36]. Table 1 shows the velocities measured at entry and exit at 7.5 cm away from either side of the whole masks and their individual layers. The layers were clamped and sealed within the two halves of the air duct mask container. Filtering efficiency was calculated from the average reduction velocity between the two measurement positions using the following equation: [\((vo-v1)/vo\)], where \(vo\) is the average velocity within the profile that increases from zero at the air duct interior surfaces to the maximum at the central measurement point. The \(vo\) and \(v1\) were taken from the micromanometer measurement for the mask's layers and the whole mask. The final V was calculated from the equation in Section 2.1.3, \"velocity measurement using pitot tubes\". An average velocity (\(\overline{v}\)) for this profile was taken to be 1/3 of the peak measured value. Also, Table 1 shows the average pore size for individual masks' layers as well as for the whole mask. These are to be compared with the droplet size ranges, from 1 \(\upmu\)m to 10 \(\upmu\)m, observed in the magnified images from the SEM of aerosol-sprayed surface particles (Figure 3). Generally, the greater the pore size of a layer, the greater is the exit velocity (\(\
u\)1). The calculated velocities in Table 1 were checked by a second calibrated instrument providing velocities \(\
u\)o and v1 directly. The 15-cm separation between the pitot tubes at positions 0 and 1 amounted to a negligible contribution to the potential energy exchange (2g \(\times\) (\(\Delta\)h)) = 2.943 m\({}^{2}\)/s\({}^{2}\)). Also, Figure 3 shows the micro-particle distribution from an aerosol spray at magnification indicated for _Surgical_ (a,b), _Reusable Cotton_ (c,d), _FFP2_ (e,f), _FFP3_ (g,h), _Antiviral_ (i,j), and _Silk_ (k,l) masks. Some particles appear dispersed in Figure 3(a,e,i) while others have combined to a larger size (Figure 3(b,f,j)). Dispersion among the multiple cotton fibers  
Figure 2: SEM images of six different mask surfaces. (**a**,**c**,**d**) Surgical, FFP2, and FFP3 with randomly orientated fibers. (**b**,**e**,**f**) Reusable cotton, antiviral, and silk with woven or ordered fabrics. (**g,h**) Graph showing the pore sizes and fiber diameters of masks. appears in Figure 3c,g,k and on a single fiber in Figure 3(d,h,l). The random orientation of non-woven fibers (_Surgical_, _FFP2_, and _FFP3_) allows passage of small-size particles more easily than the ordered woven fabrics (_Reusable Cotton_, _Antiviral_, and _Silk_).