Dr. Ravina Kullar, an infectious-disease specialist, epidemiologist, and spokesperson for the Infectious Diseases Society of America, says the “KF” in KF94 stands for “Korean filter,” and the “94” indicates a 94 percent filtration efficacy.

Differences:
You might assume that, because of the one percent difference in efficacy rates, other flat beak masks do a better job. But “there are no head-to-head trials [between the two],” says Dr. Aaron Glatt, chief of infectious diseases and hospital epidemiologist at Mount Sinai South Nassau. He says what matters more is how tightly each mask fits your particular face shape and size.