What makes an efficient mask? A couple of factors, but the major one is: Does it pass The Candle Test? Masks that allowed us to blow out a candle (like left) did not have sufficient barrier efficacy, while masks that prevented us from extinguishing the candle (like right) passed this effectiveness test, preventing our breath from passing right through them. Read our favorite masks and our full review: https://cooks.io/3hCnk2N | America's Test Kitchen