Breathability & Filtration Efficiency Compared to N95 & Conventional Masks

Breathability and Filtration Efficiencies of Other Face Coverings

Mask shortages during the COVID-19 outbreak resulted in make-your-own face coverings out of common woven fabrics in addition to designs from companies outside of the PPE industry who re-tooled their manufacturing operations to meet demand. We tested more than 50 such surgical mask and gaiter designs not certified by the FDA or NIOSH that incorporate some fit modifications and appealing stylistic features. The table below summarizes particle counting and pressure drop testing on a sampling of these devices representing the range of materials, designs and claimed filter efficiencies.

Breathability, measured as pressure drop, was performed as previously described. All devices were tested with a “Perfect seal” (glued around the edges) and by “Practical fit” over the manikin.  These devices have similar construction using 2 layers of fabric and a middle pouch for insertion of disposable filters made from a non-woven matrix described as “nanofiber” or PM2.5. While the inclusion of a non-woven insert might seem a logical way to improve filtration efficiency, in practice the large pressure drops cause both inhaled and exhaled air to take the path of least resistance around the filtration matrix resulting in poor efficiencies. Devices D & E are commercial gaiter-like designs relying solely on size exclusion filtration. Promotional literature for these 2 devices claims bacterial filtrations of greater than 99% determined using the FDA BFE standard test protocol STP0004 specifying a glued seal over the testing apparatus. “Practical fit” testing on the manikin to better represent actual use performance gave filtration efficiencies of 52% & 26.2%. This observation shows that reduced breathability compromises filtration efficiency. Beware of devices claiming high filter efficiencies determined under conditions of a "Perfect seal" as this overestimates actual performance efficiency and will give a false sense of security.