Whether you wear one mask or two, one of the most important things is to make sure it fits properly. If you went out in the rain with a coat that was too small or didn't zip up properly, you'd understand why you were shivering and soaked. Same thing here. #WearAMask #WearTwoMasks #WellFitMask

Federal health officials emphasize proper mask fit to protect against coronavirus variants, urging double masks in some cases

CDC also found that improving the fit of a single surgical mask boosted protection.
By Lena H. Sun and Fenit Nirappil

https://www.washingtonpost.com/health/2021/02/10/cdc-double-masks-covid/