What you need to know about 13 common mask types

Gaiters have become increasingly popular as a face covering during the pandemic. But despite their stylish look, and capacity for warmth in winter, neck fleeces, aka gaiters, were shown in the Duke study to separate large droplets into smaller ones that remain airborne longer.

But another study from a mechanical engineering professor at the University of Wisconsin–Madison noted that gaiters with both a nose piece and an elastic cord to create a more-snug fit actually performed better than other options.

Until we have more data, you may want to save gaiters for snowboarding, skiing, and surviving brisk wintry days, unless you’re laying one over a more-protective face covering.

The study found that double-layer bandanas, though better than nothing, only filtered about 50% of droplets. WebMD called them a “last resort.” This option might make sense if you run out of the house without your usual face covering, but have a bandana handy.

Knitted masks performed more poorly in terms of droplet transmission than any other option except the no-mask control and bandana and fleece gaiter coverings. One option is to knit or crochet a mask, then add a polypropylene layer inside to up the protection level.

Though one-layer pleated cotton masks performed better than several other options, another study noted that more layers equal more protection from droplets, with a researcher recommending that “you probably need at least three layers.” Scientists also note that gaps between the mask and the face decrease the capacity of the mask to prevent COVID-19 infection, so choose a mask where the elastic creates a snug fit. If it doesn’t, one option is to fold over a bit of the elastic so it does, then stitch into place.

The single-layer Maxima AT mask used in the study is constructed with one layer of breathable polyester fabric. Its effectiveness landed near the middle of the grouping.

The “Olson-style” mask is a two-layer cotton mask that’s contoured rather than pleated, with elastic loops that go over the ears. This is one of the most popular designs used by DIY mask creators, and patterns are now readily available.

Because valved N95 surgical masks allow outward airflow from the wearer to others in his or her vicinity, protection exists primarily for the wearer. Because of this, several airlines are now banning customers from wearing this type of mask. Fitted N95 masks without a valve do a better job of protecting everyone.

Two-layer pleated cotton masks are one of the most common options from DIY makers. Scientists have reported that tighter weave, aka thread count, cotton does a better job of filtering droplets. Studies have shown that multiple layers improve effectiveness, but that mask fit and user behavior also factor into the equation. NIOSH (National Institute for Occupational Safety and Health) reported “difficulty achieving a proper fit” for respirators (not masks) with earloop designs, preferring those with headbands.

Because of the effectiveness of polypropylene in trapping droplets, the swath option was one of the more successful ones in protecting the wearer and those around them. But a proper fit is key: Those who choose this type of protection need to take care to avoid gaps between the covering and the face. Fabric construction is also important: Polypropylene spunbond has a filtering efficiency of up to 6%, better than many other materials.

One of the benefits of polypropylene, used for the study's two-layer apron-style masks, insertable filters, and the previously-mentioned swaths, is that the material has an electrostatic charge that traps droplets. Other materials do not retain that charge when you exhale.

The type of cotton/polypropylene mask tested in the study had two layers, with a pocket where one can insert a polypropylene filter. One scientist noted that adding a two-layer polypropylene filter doubled protection, compared to just the two-layer cotton mask.

Three-layer surgical masks have the same pleated construction and elastic ear loops used in many of the cotton masks but are less effective when wet from exhalation, so they’re more of a disposable option. Their effectiveness in the study almost matched the fitted N95 masks.

N95 masks were quickly identified as being one of the most-effective tools for preventing COVID-19 transmission or infection, but because of the need for them by first responders, including medical professionals, access to them rapidly disappeared. Faced with the shortages, one nurse created an alternative.

The N95 mask used in the study, with a fitted shape and no exhalation valve, proved most effective in avoiding droplet transmission.