KF94 masks, the Korean version of an N95 mask, are gaining popularity in the United States, with experts calling for upgraded protective options over cloth masks as the omicron variant of COVID-19 continues to spread rapidly throughout the country.

Michael Baym, an assistant professor at Harvard Medical School shared his review of using KF94 masks produced by Korean firm Dr. Puri. “They’re very comfortable. I was also happy to see on the CDC/NIOSH testing page that they test at over 99.85 percent filtration, substantially better than most N95s,” he said via Twitter.

The NIOSH refers to the National Institute for Occupational Safety and Health, the US federal agency responsible for conducting research and making recommendations for the prevention of work-related injury and illness.

Kim Seung-ah, 40, a therapist at a psychiatric clinic in Seattle, said she has noticed an increase in people who prefer KF94 since late last year.

“We had a meeting because of masks at the company today and there were people who wanted to order KF94s as they find them the most comfortable,” she said.

KF94s have four layers of filtration against a typical three-layer cloth mask, but are cheaper, more breathable and more comfortable against sensitive skin than a lot of N95s.

“KF94s seem to be more readily available than the N95, less expensive (generally under $2 each) and easier to use for many people,” Stephen Morse, an epidemiology professor at Columbia University, was quoted by NPR as saying. “KF94 is actually intended for public use. In Korea, they are often worn by ordinary citizens to filter out dust or pollution."

The newfound interest in KF94 comes as the US Centers for Disease Control and Prevention considers a recommendation that Americans wear more protective masks in the face of the rapid spread of the omicron variant. KF94 has emerged as a desirable option along with N95 and KN95. N95s are the US standard, while KN95s are the Chinese standard for these close-fitting filtration devices. Both are rated to filter out and capture 95 percent of tiny 0.3 micron particles in the air.

Due to concerns over medical-grade mask shortages, US experts initially urged the public not to buy them to ensure a supply for health care providers.

But the rising Covid-19 cases and hospitalizations in the country prompt experts to advise Americans to upgrade their facial coverings.

Los Angeles County Department of Public Health said it recommends higher-level medical or surgical grade masks to reduce the risk of catching and transmitting COVID-19.

“We recommend double masking with a medical mask or wearing a KF94, N95 or KN95 mask for the best protection,” it wrote on its Twitter account Thursday.