In the meantime, some of the void is being filled by legions of sewers, called to duty in a matter of days via social media and word of mouth, their skills no longer taken for granted or dismissed as a mere hobby. They are working in living rooms, at kitchen tables and inside shuttered storefronts. They are making masks for America, much as a previous generation manufactured ammunition and tended “victory gardens” during World War II.

“Sewers, we’ve always stepped up and done this thing,” said Denise Voss, the head of the Inland Empire chapter of the American Sewing Guild. “We’re made for this time. We’re happy to stay home and sew. And we all have stashes of fabric.” Her group, with about 130 members in Southern California, is making hundreds of face masks at the request of the Riverside University Health System Medical Center.

Homemade masks are no substitute for the high-grade N95 masks that are the most effective devices to filter out the coronavirus. They’re not even as tough as surgical masks that, until recently, were plentiful in any hospital or doctor’s office.

But the D.I.Y. pieces — generally stitched together with a few layers of cotton, elastic straps and, on ambitious designs, a flexible bridge over the nose — offer at least some protection. “Better than nothing” has become a popular phrase in the tight-knit sewing community. Some doctors are wearing the homemade fabrics over surgical or N95 masks, trying to prolong the coveted masks’ limited life spans. Other masks are being handed out at health clinics and nursing homes.

“It frees up the surgical masks for the people who are the highest risk,” said Dr. Nicole Seminara, a doctor at NYU Langone Health who is volunteering in the coronavirus ward. Dr. Seminara started a social media campaign, Masks4Medicine, to solicit homemade masks from the public.