Don't use regular fabrics for high filtration washable masks

July 19, 2021

Don't use regular fabrics for high filtration washable masks - impossible breathability

Satin (polyester) from sheets from Amazon is the test material. I made six layers into a mask for Aaron Collins to test. I used the Rag Mask Max design and Aaron reported no detectable leaks - at least for his face.

After washing the mask, Aaron found a layer would be 19% filtration efficiency (F.E) at 65nm. You can't add six layers together to get "over 100%" it doesn't work that way. There is a layering formula and each additional layer gets you closer to 100% but less and less so.

The six layers Aaron tested isn't great for breathability. The fabric does pull onto your nostrils and lips as you breathe in. Any more layers and it would require something to force 3D cupping. I personally wasted nine months trying to engineer something that would make that happen.

Two layers is more breathable but only gets you 30% filtration efficiency. That'd be OK for a quick dash into a high ceiling store for a purchase among people of unknown infection.

Seventeen layers would nearly get you 95% protection (ignoring side leaks) but you would suffocate or give you lungs and chest muscles an extreme work out trying to draw breath.

Or seventeen layers for that 95% F.E. would require much more surface area. Say a grapefruit sized area that'd be held out from your face on a frame but wholly under the fabric with good edge seals. If you managed to make that you'd be rebreathing your own exhaled C02 more than you'd want, making you have to increase your flow rate to get enough oxygen in.

Or the seventeen layer mask would have to be super pleated or extreme origami to make a larger surface area between the inside and outside of the mask without the corresponding large volume. Like this: