A handful of airlines, mostly in Europe, have banned cloth face coverings in favor of higher-standard versions including surgical masks or respirators. Last month, Finnair joined a list that includes Air France, Lufthansa, Swiss International Air Lines and Croatia Airlines.

“The health and safety of our customers and crew is our first priority, and fabric masks are slightly less efficient at protecting people from infection than surgical masks,” Finnair spokeswoman Heidi Lemmetyinen said in an email. The airline allows surgical masks and filtering respirators such as FFP2 or FFP3, as well as others that are equivalent to the N95 standard…

Experts say it’s a smart idea for more airlines to get specific about the types of face coverings they allow and to only allow those that meet high standards.

“It is very important because different masks have different filtration capabilities,” said Purvi Parikh, an immunologist at NYU Langone Health, in an email. “A plane is a place that is indoors and many people in a close space and very difficult to social distance — so masks can make a big difference especially with the delta variant.”