Everything you need to know about non-woven polypropylene, the fabric now recommended for use as a filter in cloth face masks: What it is, what to look for and where to find it.
Fast tests can help keep people out of the water when it’s unsafe, and let them back in sooner once the coast is clear.
Paul Fisher
Even the best engineered filters get clogged eventually. Fish mouths have evolved structures that create unique fluid dynamics patterns that solve that problem.