What to look for in a face mask, according to science

In a matter of weeks, face masks went from being considered unnecessary and possibly harmful to mandatory in many parts of the US. USA You are forgiven if you have a little whiplash.

Currently, the scientific consensus is that face masks are at least somewhat effective in preventing the spread of COVID-19, and both the World Health Organization and the Centers for Disease Control and Prevention recommend using a cloth face covering. . But which mask should you choose? The hand-stitched one your father-in-law made as good as the one produced by your favorite fashion retailer? Are disposable surgical masks that good? How many layers of fabric should I have?

To help you navigate through the mountain of options, we’ve taken a look at the (certainly limited) science available and talked to experts to create a science-backed guide to mask shopping.

Do I need to wear a mask?

Unless you are under 2 years old, have a specific medical condition that makes it difficult for you to wear a mask, or can keep six feet away from other people at all times (hello, hermits!), You must wear a mask every time you go out from home, according to current recommendations from CDC, WHO and public health experts. And it may be a requirement in your city or state.

What does a mask do?

We now know that the main way the new coronavirus is transmitted is through respiratory droplets – small bits of saliva and other materials that are expelled from the mouth and nose by sneezing, coughing, speaking, or breathing. If you are carrying the virus, it can catch on these drops and spread to surfaces or other people, entering through the nose or mouth and causing infection. A mask can physically prevent these drops from traveling beyond your face. While they can also provide some protection against COVID-19, there are many ways to come in contact with infectious droplets (touching a surface where the droplets have landed or droplets falling into the eyes or skin), but there are fewer ways to spread the droplets (probably only through mouth and nose) Because of this, masks do a much better job of preventing an infectious person from spreading the disease than protecting a healthy person from getting it. Wearing a mask is about not spreading the virus yourself rather than protecting you.

“You use one to protect me and I use one to protect you,” said Dr. Scott Segal, an anesthesiologist at Wake Forest Baptist Health in North Carolina, who has conducted laboratory tests of mask materials.

Should I go disposable or reusable?

In laboratory tests, disposable surgical masks work well for both breathability and blocking respiratory drops. Depending on the material, both types of masks can be equally effective and safe. But disposable masks are actually only designed to be used once they are thrown away (they start to break down and become less effective after use), which is not great from an environmental perspective. Piles of single-use personal protective equipment have already accumulated on the coasts. If a disposable mask is the only option, use it, but a reusable, washable mask is a better long-term solution.

Which material is better for a reusable mask?

Many scientists have been trying to figure this out, and the answer is not exactly straightforward (is there something straightforward when it comes to COVID?). Different researchers have established devices that spray tiny droplets onto the fabric and then measure the amount that passes through the other side, while measuring air flow to determine breathability. What they have discovered is that it is less about the type of fabric (cotton, linen, silk) and more about the quality of the fabric, according to Segal. Higher quality fabrics have a tighter weave and a thicker thread that better blocks droplets.

But you also want the fabric to be breathable, according to Taher Saif, a mechanical engineer from the University of Illinois who has been researching the material of the face mask. Saif said that if the breath can’t get through the mask, it will find another way out, allowing the breath drops to spread.

“Imagine you take aluminum foil and make a mask for him,” Saif said. “All the air will be forced out the sides. If you sneeze or cough, most of the drops will escape from one side and you will lose the tip of the mask. ”

Therefore, you should be able to breathe comfortably through the mask. But measuring exactly how effective a specific fabric is at blocking drops requires a laboratory, and just because a laboratory finds that a mask made from a 100 percent cotton T-shirt is effective does not mean that the cotton T-shirt you have in your drawer It is the same material. Instead of more accurate measurements, Segal offered a general rule: hold the material in bright light.

“Look at the light coming through the fabric,” said Segal. “If you describe the individual fibers and can see the light through the fabric, it probably won’t be as effective. The less you see, the better the filter will be. “

How many layers is better?

Based on previously published or published research, two layers do a better job than one, and three layers do a better job than two. Take a look at these two videos from Saif’s studio, comparing the same jersey material in one layer versus two:

In its guidelines, the WHO recommends a minimum of three layers, and many major manufacturers appear to be using this as a general rule. So why not go four layers? You could, but remember that you don’t want to sacrifice breathability (see above). Still, choosing a mask with more layers will generally add more protection.

Does the thread count?

Thread count refers to the number of threads per square inch of fabric, but more isn’t necessarily better, according to Segal.

“Satin sheets have a super high thread count, but you can barely breathe through them because it’s so tight,” Segal said. “That may have to do not only with thread count but also with tissue tension.”

What style should I buy?

The most effective masks are those that cover both the nose and the mouth and form a somewhat tight seal at the edges of the mask. Without a professional-grade mask like an N95 respirator, you’re not going to get a watertight seal, but that’s fine, we’re looking good enough, not perfect. For everyday use, the experts I spoke with said that a comfortable but comfortable mask does the trick.

Should I buy by hand or mass produced?

The effectiveness of the mask has more to do with the material than if it was made in a factory or on your kitchen table. Even the homemade, seamless t-shirt masks have performed well in laboratory tests, especially when made with multiple layers. Review the material and choose (or make) the mask that is most comfortable for you and that you can use.

What about those exhalation vents?

Exhalation vents were designed for masks that have a very different purpose than we should be using now. These masks are designed to prevent the user from inhaling particles, not to prevent them from exhaling particles, so the vents make it easier to breathe and at the same time prevent bad things from entering. With COVID-19, the masks are meant to block your breathing from getting particles outside, not to prevent other things from entering, so an exhalation vent defeats the mask’s purpose.

What if I choose the wrong one?

At the end of the day, many experts also say that covering your face is better than not covering your face. Do your best to find a mask that is breathable and you don’t mind wearing, and you should be in good shape.

To clarify the point, Saif held up a Kleenex during our video interview and said, “Even this would be better than nothing.”