The Centers for Disease Control and Prevention found that doubling up on masks or tightening the fit of a single mask can drastically cut down on aerosolized transmission by about 95%.

“In the study … well-fitting masks provided the greatest performance both at blocking emitted aerosols and exposure of aerosols,” CDC Director Rochelle Walensky said on Wednesday. “Having both the source and the receiver wear masks modified to fit better reduced the receiver’s exposure by more than 95% compared to no mask at all.”