While a simple face covering can reduce the spread of coronavirus by blocking outgoing germs from coughs or sneezes of an infected person, experts say there is more variation in how much homemade masks might protect the wearer from incoming germs, depending on the fit and quality of the material used.

And while the degree of filtration for some homemade masks seems low, most of us — who are staying home and practicing social distancing in public — don’t need the high level of protection required for medical workers.

The biggest challenge of choosing a homemade mask material is to find a fabric that is dense enough to capture viral particles, but breathable enough that we can actually wear it.

The best medical mask — called the N95 respirator — filters out at least 95 percent of particles as small as 0.3 microns.

By comparison, a typical surgical mask — made using a rectangular piece of pleated fabric with elastic ear loops — has a filtration efficiency ranging from 60 to 80 percent.

An allergy-reduction HVAC filter worked the best, capturing 89 percent of particles with one layer and 94 percent with two layers.

video, but adding several layers of filter material inside a bandanna.

A 600 thread count pillow case captured just 22 percent of particles when doubled, but four layers captured nearly 60 percent.

A thick woolen yarn scarf filtered 21 percent of particles in two layers, and 48.8 percent in four layers.

The best homemade masks in his study were as good as surgical masks or slightly better, testing in the range of 70 to 79 percent filtration.

Homemade masks that used flimsier fabric tested as low as 1 percent filtration, Dr.

The best-performing designs were a mask constructed of two layers of high-quality, heavyweight “quilter’s cotton,” a two-layer mask made with thick batik fabric, and a double-layer mask with an inner layer of flannel and outer layer of cotton.

Browning said most sewing machines can handle only two layers of fabric when making a pleated mask, but someone who wanted four layers of protection could wear two masks at a time.

Wu, who is known for her breathtaking folded artwork, said she began designing a folded mask out of a medical and building material called Tyvek, as well as vacuum bags, after her brother in Hong Kong, where mask wearing is common, suggested it.

The scientists who conducted the tests used a standard of 0.3 microns because that is the measure used by the National Institute for Occupational Safety and Health for medical masks