We developed two options for the filter assembly, which forms the whole front section of the facegaiter. Both alternatives have three layers, filter at a high level, minimise leakage and address other key considerations. Both filter options make the facegaiter more breathable than a respirator.
Filter A provides extremely low air flow resistance and is highly durable, retaining high performance after hundreds of washes. Filter B is also highly durable and more breathable than a respirator but slightly less breathable than Filter A. Filter B's filtration performance is higher than Filter A's for the very smallest particles, and is similar to an FFP2/N95 respirator.
A suitable filter needs to do more than capture the particles of concern. Additional considerations for mask filters include:
We tested facegaiter prototypes against common measures of mask effectiveness, e.g., breathability and filter performance. They compared well to benchmark solutions, but there were other aspects to measure.
The facegaiter was conceived as an integrated solution whose whole would be better than the sum of its parts: specifically, the tubular shape also used a plenum (formed by unique stitching) working with an oversized three-layer filter to manage air flows, and there were engineered seals to minimise gaps and leaks. Therefore, we also assessed performance “as a whole” and “as worn”.
To test “whole mask” performance, as worn, a facegaiter (with Filter A), a respirator (N95/FFP2), and medical face mask were tested for wearer protection on a breathing manikin placed within a 400-liter test chamber. The setup was run with two challenge aerosols: 12% NaCl dried particles (not discharged to Boltzman equilibrium) and DEHS liquid particles (zero charge). The breathing rate was 30L/min tidal (mild exercise) with a peak flow of approximately 94L/min. Masks were first tested ‘naturally fitted’ to determine Total Inward Leakage then re-tested with the edges taped to prevent all edge leakage and measure filter performance alone.
Results suggested effectiveness similar to that of a respirator. These test results are summarised in our May 2022 poster presentation at the biennial conference of the International Society for Respiratory Protection (ISRP).
|facegaiter (filter A)|
after 100 wash cycles
|Sample 1 (off seam)||Sample 2 (off seam)||Sample 3 (off seam)||Sample 4 (off seam)||Sample 5 (off seam)||Threshold (EN14683)||Result|
|Bacterial filtration efficiency (BFE) %||99.64||99.7||99.37||99.85||99.91||< 98||Pass|
|Number of wash cycles||Test filter B||Sample Number 1||Sample Number 2||Sample Number 3||Sample Number 4||Sample Number 5||Sample Number 6||Sample Number 7||Sample Number 8||Sample Number 9||Sample Number 10|
|Airflow Resistance (mm H2O)||3.9||4.0||4.0||3.4||3.9||3.9||3.9||4.0||3.8||3.8|
|Airflow Resistance (mm H2O)||4.8||4.2||4.9||4.5||4.5||4.2||4.2||4.4||4.8||4.2|
|Filtration efficiency % (0.3-0.5um)|
|Motion type||N95 Control||facegaiter - filter A|
|test run 1||test run 2||test run 3|
|Jaw Up & Down||92.9||86.5||84.7||88.4|