Its quilted, three-layer construction is designed ... of 50 respirators—and all N95 masks—provides a minimum of 95 percent ...

The rule isn't foolproof, but it should help weed out masks that aren't very protective. The Centers for Disease Control and Prevention recommends multi-layer cloth masks for the general public.

Nasseri said layers are key to making an effective mask. It's also important that the mask forms a snug seal over the mouth and nose so that particles can't get in through gaps. "Masks with a ...