A seller already was selling a mask to simulate high altitude running. Oddly this one makes no claims about filtration.
https://smile.amazon.com/VO2MAX-Training-Mask-Simulation-Resistance/dp/B07YC6RSNV/ref=sr_1_29?dchild=1&keywords=n95&qid=1589742170&sr=8-29 https://x.com/mistersql/status/1262093773833736192
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May 17, 2020