When someone puts on a mask for the first time, chances are they don’t understand exactly how it works. Masks are used to stop the spread of small respiratory droplets that come out of people’s mouths when they do things such as cough, sneeze, or talk. If the droplets are very small they’re called aerosols. Aerosol particles can carry the COVID-19 virus. The particles invisibly fly all around the space the person is in, most of the time without anyone realizing. Sometimes the particles fall to the floor, but they can easily end up going in the mouth or nose of someone else, especially if the other person is close to the person who the particles came out of. If there is good ventilation and social distancing, more particles will go to the floor than to other people.

There are different sizes of aerosol particles, and the size of the particle affects how well it travels through a mask. There are larger particles, medium size particles, and smaller particles. The coronavirus is most similar in size to smaller particles, but it usually travels on big particles. Particles are measured in microns, a minuscule unit of measurement. In fact, one micron is so tiny that a penny is almost 20,000 microns across. Large particles are larger than 0.5 microns, medium particles are between 0.5 microns and 0.1 microns, and small particles are smaller than 0.1 microns.

If people are wearing masks, these tiny aerosol particles have to navigate through a maze of fibers in the masks to spread between people. Physics affects how well mask fibers can stop different-sized particles from entering the air.  Large particles are the easiest to trap because if the airstream brings them within touching distance of a fiber, momentum causes them to slam into it. Small particles are thrown around by air molecules in a zig-zag pattern, which increases their time in the maze, and therefore their chances of being caught by fibers. Medium size particles are the most likely to get through the mask because they’re the most likely to stay on the airstream. They evade capture because they’re small enough that they don’t have enough momentum to get thrown off course but big enough that they won’t be tossed around by air molecules.

One thing to keep in mind is that no matter what kind of mask one has, shape and fit can have a large effect on a mask’s effectiveness. If there’s space between a mask and a person’s face, it can make the mask much less effective; this includes when a mask is prevented from going around someone’s chin by facial hair. Good masks have a large surface area, fit snugly against a person’s skin, and leave space around one’s nostrils and mouth. More surface area can be better because it creates a large breathing space and the likelihood of a particle getting caught in a fiber increases.

The ideal mask is an N95 that fits well, but if everyone wears a mask no matter the type, efficiency increases because particles have to make it through two masks. For instance, if 75% of the particles one person exhales make it through their mask, the particles will most likely not be inhaled by the other person wearing a mask. Only some particles will make it to the other person, and their mask would filter the remaining particles, making it so only a few get through. Some masks have valves for breathing out, but the valve doesn’t filter aerosols like the rest of the mask does. These valves do little to protect others and can increase the risk to others.

N95 mask fibers are much more tightly woven together than most common fabrics such as cotton. According to the New York Times, “[N95 mask filters] are made of synthetic material, vary in size, and are arranged randomly… they have an extra feature: an electrostatic charge that attracts and captures particles of all sizes.” N95 masks filter 95% or more of medium particles and filter even more of particles of other sizes. According to Dr. Deb Savage, a local chemical engineer who has volunteered for a COVID-related non-profit, “N95 respirators are regulated by the US government; they are tight-fitting and must be tested to prove that they protect the wearer against at least 95% of 0.3-micron size particles.”

Surgical masks are the kind of mask that doctors and nurses wore before the pandemic. They are disposable, cheap, and sold in bulk, which can make them useful, but they are loose-fitting. Like N95 masks, they are regulated by the US government, but they are not required to be 95% effective, though manufacturers do have to test them.

People who don’t work in the medical field normally wear cloth masks. There are some cloth masks that are made by companies, but many are made by craftspeople. Many materials and fabrics have been tested to see if they’re effective. Studies generally show masks made of multiple layers or tightly woven fabric work better than other masks in reducing the spread of COVID. If one-layer masks are going to be used, it is recommended to wear two of them at the same time.

One type of mask that there has been a lot of controversy over is gaiter masks. Gaiter masks are thin, stretchy, and tend to go right up against a person’s skin. Gaiter masks are made with the intention of being used during sports and are therefore very breathable. Many experts say that they are not very effective, and should not be used unless they’re the only option available. According to Dr. Savage “ … a single layer of stretchy knit neck gaiter, for example, would not be very protective, although it would be better than nothing at all.”

Dr. Savage recommended the HALOmask. In an interview with the Insider she remarked,“[My family’s] favorite mask is the HALOmask because it is made of a dual-layer of fabric with an insertable filter tested by Nelson Labs to be 99% protective for particles down to 0.1 micron. The masks are super comfy and breathable even with the filter inserted. Each mask has a bendable nose piece and adjustable straps, and there are four different mask sizes to choose from.”

Overall, here is what the reader should understand about masks. Masks have fibers in them that catch COVID particles, and the fibers in some masks are woven differently than others. If more people wear masks then fewer particles will be spread. N95 masks are the best kinds of masks for preventing the spread of COVID.