Although we’re all excited by the steadily growing number of people getting their Covid-19 vaccines, it’s not quite time to retire our face masks just yet. We still need to keep using them as we wait to make sure the country reaches full herd immunity. In the meantime, there’s good news for those who prefer wearing reusable cotton masks: They work better the longer you wear them!
Researchers from the National Institute of Standards and Technology (NIST) and the Smithsonian’s Museum Conservation Institute tested several different fabrics commonly used for face masks to see how they held up to humidity levels similar to what we produce while breathing in them. They compared synthetic fabrics, like rayon, polyester, and spandex, versus cotton and surgical masks.
Their results showed that exposing masks made with cotton to humidity improved their filtration efficacy (or how well the material catches particles) over time. In fact, it increased by 33 percent in the same conditions we’d create while wearing a cotton mask for any prolonged period — like tossing it on to run errands. The researchers also said this improved filtration didn’t hinder the ability to breathe through the fabric.
The synthetic fabrics, on the other hand, had lower filtration efficacy to begin with and showed no improvement after exposure to humidity. Surgical masks were about as effective as cotton masks, but didn’t show the same type of improvement over time (but didn’t get any worse, either).
The video below shows the difference between a cotton mask that has been exposed to humidity (left) versus a fresh mask that hasn’t been exposed to humidity yet (right).
That’s a pretty compelling visual! Basically, the longer you breathe in a cotton mask, the better the barrier becomes. The researchers note that this backs up their previous study that found cotton masks more effective than synthetic fabrics in dry conditions, too.
Remember, even if you’ve been fully vaccinated and waited for your own immunity to build up, it’s still important to wear a mask while out and about. The vaccines are only 95 percent effective, meaning there’s a 5 percent chance some particles can make their way to you. You might not get sick, but you could pass those germs back around to others who will have worse reactions. And it’s always better to be safe than sorry!