The term “medical-style mask” refers to the types of masks you typically see in health-care settings. These include respirators, such as those labeled N95 (designed to meet US standards), KN95 (Chinese standards), KF94 (Korean standards), and FFP2 (European standards), as well as surgical-style masks—the pleated variety with ear loops or ties that typically come in boxes of 50 or so. Consisting of high-efficiency filter layers, all of these mask types are designed to protect the wearer in high-risk situations. (Cloth masks, in contrast, were initially intended to protect other people from the wearer, though depending on their materials and design, they can also work the other way around.)

If you’re spending time among others indoors, visiting a hospital or clinic, or caring for a COVID-19–positive person (or someone who is vulnerable to a severe case of COVID-19), you may consider wearing either a respirator mask or a surgical-style mask modified to form a better seal or layered under a well-fitting cloth mask. In fact, a CDC paper reported that securing a surgical mask to the face (by knotting the ear loops and tucking in the sides, as shown in this video, or by adding a well-fitting cloth face mask over it) can potentially decrease your exposure to possibly infectious tiny airborne droplets called aerosols by about 95%, which is also about how well respirators are expected to perform.

This level of filtration on medical-style masks (assuming they’re genuine) is better than what you can get from almost all masks made from only cloth, said Linsey Marr, a professor of engineering at Virginia Tech who is an expert in the science of aerosols. In fact, when Wirecutter commissioned cloth-mask filtration-efficiency testing, filter-less, double-layer cloth masks filtered (at a flow rate similar to what happens with normal talking volume) around 47% of 0.5-micron particles at best. (Those with incorporated filters, however, such as the Enro Tech and Happy Masks Pro, filtered similarly to N95s.) If you’re not vaccinated, Marr “highly recommends” bolstering your well-fitting cloth mask, whether by wearing a surgical-type mask beneath it or including a good filter inside it. Vaccinated people may choose to do this as well, depending on the circumstances.

Constructed with multiple layers of nonwoven fabric, an N95 respirator blocks out at least 95% of particles as small as 0.1 micron in diameter. Surgical N95 respirators offer the added benefit of also having passed tests for such factors as fluid resistance, biocompatibility, and flammability. All legitimate N95 masks are approved by NIOSH as respirators; surgical N95 models have undergone additional NIOSH testing to meet specific FDA requirements.

N95 masks fasten snugly to your face with two bands that go around the back of your head. As with cloth face masks, some people find bands to be easier to adjust than ear loops—you can play around with knots and positioning to create a good seal. However, an N95’s elastics tend to be tighter than those on cloth masks, which some wearers might find suffocating. Some N95 masks, like Wirecutter’s picks for dealing with smoke and dust, have valves for easier exhalation, but because they let unfiltered air escape, they are not useful in preventing the spread of the coronavirus.

KN95 masks (China’s N95 equivalent) should block out 95% of 0.3-micron particles; KF94 and FFP2, 94%. All are made with similar layers of high-filtration, nonwoven materials. KN95, KF94, and FFP2 are internationally sourced respirators and therefore don’t undergo the NIOSH approval process. Earlier in the pandemic, with N95 respirators in short supply, some of these masks—if they met certain criteria—were FDA-cleared for workers in health-care settings under an emergency use authorization (EUA). That authorization has since been revoked (PDF) due to a replenished supply of N95s, but the FDA suggests that these previously authorized respirators (such as our pick, the Powecom) be redistributed for use in nonmedical settings.

Unlike N95 masks, these other respirator masks typically have ear loops instead of headbands. People often encounter good filtration but a bad fit when shopping for a KN95. The same goes for N95 masks that aren’t customized (as they typically would be in a hospital setting). A January 2021 PLOS One article on mask-fit issues reported that a KN95 was a poor fit for all seven study participants, while the five N95 masks in the experiment did little better—failing to fit four out of seven subjects. Even a bit of extra fat in the chin or a few millimeters in the width of the nose can have an impact on a respirator’s fit, the authors noted.

Loretta Fernandez, PhD, associate professor of civil and environmental engineering at Northeastern University, found that a poorly fitting KN95 may block 0.3-micron particles only as effectively as a poorly fitting surgical mask—at around 72% efficiency instead of the promised 95%-plus. This level of performance may be problematic for people working in the ICU but perhaps less so for someone doing a quick run to the post office. Still, from an economic perspective, it’s pointless to spend the extra money on a KN95 only to have it work as effectively a much cheaper mask. Fernandez, who has been assessing masks (PDF) since the start of the pandemic, noted an easy fix that a dentist shared with her: By cutting the ear loops on a KN95 mask and reattaching them to form headbands, the dentist was able to achieve a secure enough fit to nudge the filtration back up past 90%.

Surgical masks are medical devices regulated by the FDA. These masks are designed to prevent fluid from penetrating the mask (from, say, splattering as a result of a medical procedure) and potentially harming the wearer. Because they don’t fit close to the face, they’re not designed to protect the wearer from inhaling small, potentially infectious particles. Nevertheless, in order to gain FDA clearance, either through 510(k) or the agency’s emergency use authorization, surgical masks undergo testing to meet voluntary consensus standards set by ASTM International (formerly the American Society for Testing and Materials)—and those standards include achieving a level of filtration efficiency. Level 1 indicates that the mask blocks out 95% of particles at 0.1 to 5 microns in diameter at certain flow rates following another set of challenges. Levels 2 and 3 indicate at least 98% for the same particle-size range.

Medical-grade masks should be fluid resistant and should keep their shape in the rain better than most cloth masks. Regardless of which type of mask you manage to get your hands on, however, you won’t come anywhere close to the stated filtration values in real life unless you secure a perfect seal to your face around the entire perimeter of the mask. “Generally speaking, if you’re fogging up your glasses, it’s not a perfect seal,” said Hana Akselrod, assistant professor of medicine in the division of infectious diseases at George Washington University School of Medicine. (If you don’t wear glasses, take a big exhale with your mask on—if you feel a puff of air on your skin near the edges of the mask, you need a tighter fit.)