Story highlights Cotton fabrics absorb small amounts of the water in a person's breath, creating a moist environment inside the mask Cotton masks that become slightly moist through human breath are nearly 35 per cent better on average at capturing particles than when they are dry, making them a better choice than synthetic masks to stop the spread of COVID-19, according to a new study. Synthetic masks showed "no performance change" in stopping particles when humid and therefore "performed poorly" relative to cotton, the US National Institute of Standards and Technology (NIST) said of its study. "This new study shows that cotton fabrics actually perform better in masks than we thought," NIST research scientist Christopher Zangmeister was quoted as saying on the NIST website.