Assuming masks are worn properly ... just 54% of small particles and 56% of larger particles. By contrast, four layers of natural silk filtered 86% of small particles and 88% of large particles ...

Masks with four or more layers could provide 80% to 90% filtration. This means that single-layer masks, such as neck gaiters and bandanas, will likely provide the least protection. In terms of ...

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 ...