Date Time Share Study Indicates That Humidity in Breath Makes Cotton Masks More Effective at Slowing Spread of COVID-19 A swatch of cotton fabric that has been exposed to high humidity typical of a person’s exhaled breath (left) filters out more droplets than a swatch of cotton fabric that has not been exposed to high humidity (right). Credit: NIST Researchers have come up with a better way to test which fabrics work best for masks that are meant to slow the spread of COVID-19. By testing those fabrics under conditions that mimic the humidity of a person’s breath, the researchers have obtained measurements that more accurately reflect how the fabrics perform when worn by a living, breathing person.