The New York Times reported yesterday (April 5) on scientists' findings about the best mask-making materials during the COVID-19 pandemic. The main criterion used was how well each material worked to filter microscopic particles.During the materials tests, the following materials scored well:

• HEPA furnace filters
• vacuum cleaner bags
• 600-count pillowcases in layers
• flannel pajamas or similar materials

The tests listed coffee filters piled in layers as having medium-level effectiveness. The lowest-scoring materials were scarves and bandannas. However, the researchers noted that those materials were still able to capture some particles.

Light Test

There may be other materials that are effective too. The article recommends a light test to help evaluate a material's effectiveness. You hold the material up to a bright light. If you can see the light easily passing through and even see some of the material's fibers, then it's not very good.

Quilters' Masks

One study determined that good homemade masks offered a slight improvement over surgical masks. The best homemade masks, the study found, used two layers of "high-quality, heavyweight 'quilter’s cotton.'" Two layers of thick batik fabric were also good, as was an inner layer of flannel combined with an outer cotton layer.

Additional Considerations

The other thing to remember when making a mask, of course, is that the mask wearer needs to be able to breathe with the mask on. So the most dense fabrics, although they would filter out particles, might make the wearer pass out!

Also, some materials need to be layered more thickly than others. The tests determined, for example, that the 600-count pillow cases are far more effective in four layers.Finally, using air filters as a mask can be problematic because the wearer could inhale some of the filters' fibers. The only way to use air filters safely is by encasing them in cotton.Read the NYTs article here. Read about how to make a mask at home here.