The masks used to protect against COVID-19 are cloth, three-fold, and N95. Cloth and three-fold do not have tight fit, usually called a mask, but N95 does, usually called a respirator. In addition, N95 has a submicron efficiency of 95% or higher based on 42 CFR Part 84. Some three-fold masks like cloth masks do not have specifications for general use. The specifications of medical masks are based on ASTM F2100-19.

Electrostatically-charged meltblown microfiber fabrics are commonly used to achieve the specifications of the masks and the respirators. Charges can be retained for longer than ten years. Depending on the charging method, the efficiency can be ten or 20 times improved compared to the uncharged one at the same basis weight and pressure drop. The measured surface charge potential shows that the charged media is a bipolar electret. Therefore, it attracts both positive and negative particles by Columbic force, as well as neutral particles by image force.

Several N95 sterilization methods have been validated by NIH, in which some will degrade the charges and/or the shape of the respirators, while others will not.

Cloth masks are primarily used to block the virus. Nowoven media can block and filter the virus. The combination of cloth sandwiched with a nonwoven filter is an ideal design of DIY masks.