The body of evidence continues to grow: masks protect the person wearing them from COVID-19, in addition to those around them. But with so many choices, what’s your best option?
Regardless of mask-type, fewer coronavirus particles get through to people wearing face coverings, according to a new paper that will be published in the Journal of General Internal Medicine shortly. Fewer particles could result in milder infections if the virus manages to slip through.
Another study, published last month, compared the COVID-19 growth rate before and after mask mandates in 15 states and the District of Columbia. It found that mask mandates coincided with slowdowns in daily COVID-19 growth rates.
Testing the effectiveness of coronavirus masks
While working on another recently published study, researchers from Duke University evaluated the effectiveness of 14 different types of masks by estimating how many droplets traveled through the mask during normal speech.
The researchers used a laser beam, a lens that turned a laser beam into a sheet of light, and a mirror that directed light into a dark box made of cardboard. People spoke the same phrase into the box with, and without a mask. The particles that hit the lens produced visible flashes recorded by a phone’s camera on the other end of the box.
“The key point of this paper is that we are proposing a very simple, easily duplicated system, where community groups could actually test masks themselves,” said one of the study’s co-authors, Warren S. Warren, a professor of physics, chemistry and radiology at Duke.
So what’s the most effective kind of mask against COVID-19?
The solid dots represent results of 10 trials for a mask by one speaker. The hollow circles represent the relative droplet counts for four speakers.
1. Fitted N95 mask
Medical N95 mask with no exhalation valve proved to be the most effective. However, the CDC asks the general public to not wear N95 respirators, which are limited in supply, so they can be reserved for health care workers and first responders.
2. Three-layer surgical mask
When study participants said the phrase “stay healthy, people” wearing a three-layer surgical mask, only a tiny fraction of droplets got through.
Surgical masks are single-use only, and are made to protect the wearer’s nose and mouth from contact with droplets, splashes and sprays that may contain germs. They also filter out large particles in the air.
3. Cotton-polypropylene-cotton mask
A mask made from two layers of cotton and one layer of synthetic material proved to be the most protective option aside from masks intended for medical professionals. Another recent study suggested that a homemade cloth face masks likely need two or three layers to be effective in preventing the spread of the coronavirus.
A single-layer covering reduced the droplet spread from speaking, while the double-layer covering was better in reducing droplets from coughing and sneezing, according to the researchers.
4. Polypropylene apron mask
This mask had two layers of polypropylene, a soft easy-to-clean synthetic fabric. Polypropylene is one of the most popular materials for masks because viruses and bacteria can’t live on the fabric for long.
According to a study published in Nano Letters, polypropylene may be one of the best materials for a homemade mask. It has the electrostatic charge that traps incoming and outgoing particles. It loses its electrostatic charge when washed, but can be recharged by rubbing it with a plastic glove.
Researchers used a slightly damp washcloth in another experiment. Using high-speed video, they found that saying a simple phrase generated hundreds of droplets ranging from 20 to 500 micrometers. The washcloth blocked nearly all those droplets from the person’s mouth.
6 – 7. Two-layer pleated style masks
When choosing the material, make sure the cotton is woven at a high density so there are no visible pores under light, according to the study in Nano Letters. If that’s not the case, it may be best to use multiple layers.
“I wouldn’t put too much stock in the small differences that we saw between the different cotton masks; I would emphasize that fit is important,” Warren said.
8. Valved N95
Researchers noted that while the valve does not compromise the protection of the wearer, it can decrease protection of the people around because the masks release exhaled air through their openings, according to the CDC.
The CDC has also recently updated its guidelines advising Americans to avoid face masks with exhalation valves or vents because they aren’t as effective in preventing the spread of COVID-19.
9. Olson style mask
The Olson Mask Pattern was named after the nurse who created cloth masks to be used when medical masks were not available. It is curved to fit the nose and mouth area. These masks are not a substitute for N95 masks in health care environments, but they can be good for personal use.
10. Maxima AT mask
This “1-layer Maxima AT mask” may look slightly similar to surgical masks, but it doesn’t offer nearly as much protection, according to the research.
11. One-layer pleated style mask
The mask with one layer performed poorly. The WHO recommends that fabric masks have three layers: an inner layer that absorbs, a middle layer, which can be inserted in the middle to act as a filter, and an outer layer made from a nonabsorbent material like polyester.
12. Two-layer pleated style mask
It’s important to make sure the mask is properly fitted and covers your nose and mouth. Studies suggest that 60% of users fail the fitting of surgical masks on first attempt.
If the mask is loose, it allows for the significant leakage of air around the seal areas and can contribute to an exposure to aerosols. Having a mustache or beard can also make it challenging to properly fit the mask.
13. Knitted mask
For this one, researchers used a mask with a looser weave.
“Think of the fabric as being something more similar to a sock than similar to a bed sheet, which is more like what you have for the standard cotton,” Warren said.
Larger and open pores in the masks may allow more particles to get in. Washing and drying the mask may further decrease its deficiency.
Bandannas proved to be one of the least effective in the study published in June in the journal Physics of Fluids. Although a bandanna can reduce the range of particles expelled during a cough, it scores lower than an uncovered cough at stopping the smallest aerosolized respiratory droplets.
15. Neck Fleece
The neck fleece or gaiter beloved by runners ranked worse than no mask at all. It could be because the porous fabric may break the larger particles into smaller ones. Smaller particles remain in the air longer than large droplets.
However, Warren points out that the research he co-authored wasn’t a large-scale clinical trial, so the results can’t be generalized. The outcome for the gaiter was worse because some of the most comfortable masks are usually thin and those don’t do a good job of blocking particles.
“When we take a look at the gaiter we used, for example, if you hold it up the single layer to a light, stretched the way it would be when worn, you can see light through it,” Warren said. “And my feeling is that if that’s the case, it’s not doing a very good job protecting the people around.”