n April 3, after new data was released showing that up to a quarter of people infected with the coronavirus are asymptomatic, the CDC announced new recommendations for wearing face masks. Its guidelines stipulate that everyone should cover their faces with a cloth mask while “in public settings where other social distancing measures are difficult to maintain,” like the grocery store. This, of course, doesn’t mean we should rush to hoard the medical-grade masks desperately needed by health care workers. It means fashioning something yourself. The CDC specifically recommends using tightly woven cotton to make a mask. So those of...