If you are making your own face mask at home, the Army recommends using four-ply microfiber cloth, a material that can typically be found in the cleaning supply aisle.
The fabric filters out over 75% of particles, according to an Army news release.
The fabric is typically used for cleaning and polishing surfaces.
The Army’s Chemical Biological Center, which falls under the Combat Capabilities Development Command, began testing materials around the same time the Pentagon announced military personnel should begin making their own face masks.
"We knew that claims about masks and face coverings were exploding all over the internet, and we wanted to make sure that any decisions about materials . . . will be based on proven science," said David Caretti, who led the effort as the chief of the Center's Chemical Biological Protection and Decontamination Division.
The center is one of only a few agencies that is experienced in performing tests that precisely measure materials' filtration efficiencies in strict accordance with National Institute for Occupational Safety and Health standards, according to the news release.
"The challenge is to pick a material that effectively blocks the virus particles from going through the material while not being too hard to breathe through," Caretti said. "If the resistance is too high, airflow will simply bypass the covering and go around the edges.”
The test team started out by testing materials that defense and federal agencies sent in for evaluation. It then expanded the testing to materials people likely have at home. So far, 300 tests have been conducted.
The testing involves spraying a salt aerosol at a swatch of material. The team then measures the density of salt aerosol suspended in the air on one side and compares it to the density on the other side after it passes through the material.
The team also found that even a polyester bandana can be effective in filtering out 40% of particles if used in layers.