In early April, when Americans began to embrace the idea of wearing face masks to flatten the curve of the coronavirus, President Donald Trump suggested it wouldn’t hurt the public to wear masks, but that scarves could be a perfectly suitable substitute.

“It doesn’t have to be a mask. It can be a scarf,” Trump said. “What I do see people doing here is using scarves. And I think in a certain way, depending on the fabric, I think in a certain way, a scarf is better, it’s actually better.”

A new study of the best and worst materials for DIY face masks just proved he was absolutely incorrect.

Smart Air, a social enterprise and certified B-Corp that promotes cost-effective, data-backed air filters as a solution to indoor particulate air pollution, has released the results of their latest research on DIY face mask materials, in which they tested over 30 different materials ― including bra pads, coffee filters, pillow cases, electrostatic cloths, cotton T-shirts, wool, bed sheets, polyester, bandanas and more ― for their effectiveness in filtering coronavirus-sized microparticles, as well as their breathability.

Both those factors are vital, because while some materials may test high for filtration, they test low for breathability ― a mask you can’t actually breathe in isn’t exactly helpful to anyone.

Among the key takeaways: Trump’s scarves tested among the least effective materials, while denim, canvas and paper towels were among the best.