Which Face Masks Work Best?

Duke University scientists say N95 masks without valves provide the best protection while fleece and bandanas performed worst in testing.
Posted at 6:19 PM, Aug 13, 2020

N95's, cotton face coverings, neck fleeces — not all masks are created equal. New research from Duke University shows which masks work the best. 

"Yeah, that's there's lots of duct tape on this gizmo," Dr. Martin Fischer Director of the Advanced Light Imaging and Spectroscopy Lab said.

Duke chemist and physicist Martin Fischer created a test setup consisting of a box, a laser, a mirror, a lens, and a cell phone camera.

"So you have the speaker hole right here. We have the light sheet going in from the left side, going out the right side and the camera on the far end. Looking at the light sheet. And when you speak and you emit droplets and as soon as they go through the light sheet, they scatter light. So you see the flash of light that gets recorded by the video camera," Fischer said.

Duke's study found N95 masks without valves — the ones worn by hospital and health care workers — did the best.  

Surgical or polypropylene masks also performed well. Hand-made cotton face coverings provided good coverage, eliminating a substantial amount of the spray from normal speech. But bandanas and neck fleeces did not block the droplets much at all.

"It's not the case that any mask is better than nothing. There are some masks that actually hurt rather than good," Fischer said. "We attribute this to the fleece, the textile breaking up those big particles into many little particles. They tend to hang around longer in the air."

Mask wearing continues to be a polarizing issue. Some public officials now are banning masks. We asked the Duke scientists if their research muddies the truth about the effectiveness of wearing masks. Their answer: mask-wearing is a must.

"I think the general consensus worldwide is that masks work and everyone should wear a mask.  Of course we are trying to shed light on which ones are truly covering and providing barriers," Dr. Eric Westman said. "It seemed obvious to me, is that you are also protecting yourself when you are wearing it, but you are protecting other people from you, if you don’t know you have the infection."

Researchers say their work is meant to show other labs, and us, how to check how well masks work. They say a cardboard box, and a $100 laser bought online could do the same task as what they constructed.