“Our kids are pretty good about keeping masks on, but it took a day or so for them to get used to the two flaps, and every morning we pinch the nose part before they go to school so they conform to their faces,” Mr. Byun said. “Previously, our younger son would go through at least two cloth masks a day because they would get soaked, but he’s able to wear these all day because they don’t press up against his mouth. Both seem to like them and say they’re easy to breathe in.”

Dr. Ashish Jha, dean of the Brown University School of Public Health, said one of the benefits of the KF94 is that Korea imposes strict controls on mask production and approval.

For a mask to be certified by the Ministry of Food and Drug Safety in South Korea, mask makers must submit an application that includes details about product development, lab test data and evidence of product safety and efficacy. The ministry inspects several thousand masks a month to make sure they meet government standards, according to a written statement from an MFDS representative.

Although some counterfeit KF94s have emerged in recent months, overall there seem to be fewer counterfeits in the supply chain compared with N95s or KN95s, the respirator-style masks approved in China. “It’s a much, much tighter regulatory regime,” Dr. Jha said.

The penalties for selling an unapproved mask or one that does not meet standards are steep, including fines, suspension of product sales and up to five years in prison. In recent months, the ministry has been involved in several high profile crackdowns on illegal mask production and distribution. In April 2021, the agency prosecuted four people for selling 11.4 million fake masks. And in December, the ministry uncovered 16 companies in Busan, South Korea’s second largest city, that were manufacturing and selling fake masks.