“Elastomerics for us really were a game changer,” Dr. Chalikonda said. “When I think of all the millions of dollars wasted on N95s and then trying to reuse them makes you realize how much elastomerics are a missed opportunity.”

Federal health officials say they are moving as fast as possible to produce stronger guidance on elastomerics. Maryann D’Alessandro, director of the National Personal Protective Technology Laboratory, said scientists were reviewing feedback from a study that distributed nearly 100,000 respirators to hospitals, nursing homes and first-responders across the country. “If we can get a tool kit together to serve as a guide for organizations and educate the users, we hope it can help move the needle,” she said.

Many masks entrepreneurs are not likely to last that long. Max Bock-Aronson, the co-founder of Breathe99, which makes an elastomeric respirator that Time magazine included on its 2020 list of best inventions, has been winding down operations at the company’s Minnesota plant.

He blamed the slump in sales on Covid fatigue and waning public interest in protective gear. The company’s fortunes, he added, were doomed early on by the C.D.C.’s mask guidance, which prompted Amazon, Google and Facebook to limit or bar the sale of medical-grade masks to consumers, even as P.P.E. imports once again began flooding the United States.

“The whole industry has been gutted,” said Mr. Bock-Aronson. “Every time there’s a new variant, we get a small bump in sales, but I haven’t taken a nickel out of the company since last May,”

For now, he is focused on finding a buyer for his company while selling off his inventory online. The masks cost $59 and can be sheathed in washable covers that come in eight colors, among them crimson, linen and royal blue.

All sales, the website points out apologetically, are final.