Zach's fabric tests April/May
Note: Based on https://www.pnas.org/content/115/10/E2386, this page focusses on droplet and droplet nuclei particle sizes only.
A new pal - Zach (in Vermont) had tested fabrics I'd mailed from the UK in April:
The cotton was new bedding from my local supermarket - 400 thread count. The satin was a very cheap bedding set from Amazon (Viceroy brand). Look at the blue column on the right - single layer of that 400-tc cotton. Not great for the droplet and droplet nuclei particle sizes. Two layers better - but unbreathable if they were pressing against your nostrils/lips. I'd already determined that in April (pre filtration testing results). And, promoting myself to #maskTech specialist embarked on a stiffener/retainer/ribs odyssey to boost breathability. Zach's data just confirmed a need for multi-layer and tricks for breatheabilty. I went on to make multiple 6-layer satin + 1-layer 400-tc cotton masks. Those too would be in the high 90's for the particle sizes that are important.
Graph from that data:
I stopped making the 6-layer satin + 1-layer 400-tc cotton masks, and switched to 750-tc cotton (from Marks and Spencer) and 1 layer of the same satin. That's better filtration, but slightly tougher to breath through. More tweaking of the stiffener/retainer/ribs design.
The test rig Zach made for fabric testing:
There's anomalies in there. Things that should really be retested. Again - this was the start of May.
His "R95" is a N95 cut up and used as a reference - "0" for pressure change. It, HEPA, & Shop Cloth was what Zach sourced for this experiment (USA).
Duchesse Satin , Satin, and 400-tc cotton are what I mailed (UK). Duchesse is the wedding dress stuff. I'm made a 1 layer mask from that and thought it was a suffocation device - I've done nothing with the 1 yard I bought since. The other satin was Viceroy brand satin (sheets from Amazon cut up). 400-tc is cotton sheets from my local supermarket. That one layer of duchesse satin had less of a pressure drop than the cheap Viceroy satin - which doesn't make sense from my kitchen sink tests. I'd sent a third satin (from 1 yard if bought in a fabric store in Feb), but Zach missed that it wasn't one of the two others in the padded envelope, and didn't test it. Of course, I'd NOT labelled anything in the shipment.
This was before Konda et al was published in early May and we might have skipped this exercise had we known that was in progress. That said, Konda didn't test, 400-tc, 200-tc 80-tc and someone needs to.
Zach is a software industry guy too, so everything about this work needs to be re-verified in academia or the medical industry.