Three years into the pandemic, elastomeric respirators remain a rarity at American health care facilities. The C.D.C. has done little to promote the masks, and all but a handful of the dozen or so domestic companies that rushed to manufacture them over the past two years have stopped making the masks or have folded because demand never took off.

Most cost between $15 and $40 each, and the filters, which should be replaced at least once a year, run about $5 each. Made of soft silicone, the masks are comfortable to wear, according to health care worker surveys, and they have a shelf life of a decade or more.

“It’s frustrating and frightening because a mask like this can make the difference between life and death, but no one knows about them,” said Claudio Dente, whose company, Dentec Safety, recently stopped making elastomeric respirators that were specifically redesigned at the request of federal regulators for health care workers.