So in other words, "fabric masks don't work", like we've been saying since nine months ago. If you gotta wear four of them to make up for a standard ACTUAL mask, then they're worse than useless since they cause all sorts of side-effects, and apparently offer practically no benefit.

I love the NBC article's handwave of "don't use coffee filters as masks, those haven't been tested for efficacy", when clearly, fabric masks haven't either, if you gotta wear a half-dozen of 'em.