Researchers ran experiments using dummies to assess how certain modifications could improve the fit of masks and reduce exposure to aerosols.
This includes wearing a cloth mask over a surgical mask as well as knotting the ear loops of a surgical mask and tucking in the sides.
The researchers found that wearing just one mask blocked 42% of the particles from a simulated cough but that jumped to 82% if a cloth mask was worn on top of a surgical mask.
Also, they found the knotting and tucking of the surgical mask reduced exposure to particles by about 65%. But the exposure was reduced by more than 95% if both mannequins were double-masked or wore the knotted and tucked surgical masks.
The CDC updated its website Wednesday to reflect the latest information.