For the study, four common types of masks – N95 mask, three-ply disposable surgical mask, two-ply cotton-polyester mask and heavy cotton mask were studied.
The humidity levels were measured by having volunteers breathe into a sealed steel box. When people wore no mask, the water vapour from the exhaled breath filled the box, leading to an increase in the humidity inside the box.
When people wore a mask, the humidity buildup inside the box decreased greatly as most water vapours remained in the mask, becoming recondensed and being re-inhaled.
The measurement was taken at three different air temperatures, ranging from 46 to 98 degrees Fahrenheit.
To ensure there is no leakage, the masks were fitted against the volunteer’s face using high-density foam rubber. It was found that all the four masks increased the level of humidity of inhaled air, but at varying degrees.