Filtration Efficiency tests for multi-layer smart-fab NWPP
Citizen Scientist, Aaron Collins (@masknerd) tested three more masks of mine.
- Four layers of spunbond NWPP (38 gsm Smart-fab), with one outer layer of 180 TPI of poly-cotton
- Same, but with eight layers of the NWPP
- Same, but with twelve layers of the NWPP
Arron's test rig uses 65nm particles.
Pros: super easy to setup and be accurate with. So easy, he can do it live on video and not lose viewers.
Cons: this particle size is smaller than the of SARS-CoV-2 viron itself. No matter though, his test is excellent at determining best-case fit for a mask, and of how close the materials are to comparable tests for known 'good' N95 masks which perform great at that particle size. Spoiler: regular cloth masks made with normal fabrics can probably never get close to that performance and still be breathable. E.g. 20 layers of polyester satin will have great filtration, but pass no air at all.
Aaron's results and experience report
Four layers NWPP + one of 180 TPI polycottonFiltration Efficiency: 73.0%Time to Max Breath @ 0.25" H20: 2.23Pressure Drop: 0.13Quality Factor: 10.2Eight layers NWPP + one of 180 TPI polycottonFiltration Efficiency: 84.9%Time to Max Breath @ 0.25" H20: 3.02Pressure Drop: 0.17Quality Factor: 10.9Twelve layers NWPP + one of 180 TPI polycottonFiltration Efficiency: 85.7%Time to Max Breath @ 0.25" H20: 3.84Pressure Drop: 0.22Quality Factor: 8.7
Why the quest for high-filtration & washable is important
The developing world can't compete for disposable N95, FFP2 (Europe), and KF94 (South Korea) grade masks. That's a cost thing. Plus supply of those ebbs and flows. The developed world can barely afford them (hospitals, individuals).
The environment can't afford the cost of the disposables in multiple ways.
I'm using a RagMask Max design because it's quick to sew (10 mins each), but there are plenty of other designs that would have the same performance if they are tight on the face 4 layers of 38 gsm smart-fab.
Aaron's aging test equipment broke after this mega test run. He's to attempt a repair in the coming weeks.
US and UK snail-mail systems conspired to make all UK->US shipments of masks take longer that 4 weeks. That was regardless of requiring signature or not. Aarons masks (two shipments) took over a month each. Fedex would have been quicker by multiple weeks.
Joceyn Songer and the MakerMask comnunity did the pioneering work on spunbond NWPP. The test they commissions - https://makermask.org/fabric-mask-material-testing-results show that.
My predictions for effectiveness based on their test data:
Mask design and fit are key. Layering beyond 5 layers probably doesn't match predictions because of edge leaks.