The three scarves tested ― made of merino wool, cashmere and lightweight ramie (similar to linen) ― all captured fewer than 10% of smallpox-sized particles. The worst scarf material – 100% ramie – filtered just 2.8%.
The best overall materials for DIY face masks
Based on a combination of breathability and filtration effectiveness, the study recommended denim, bed sheets (80-120 thread count), paper towels, canvas (0.4-0.5mm thick) and shop towels for homemade masks.
Keep in mind, however, that paper towels are not washable or reusable.
The 0.4-0.5mm thick canvas material ranked as being easier to breathe through than a surgical mask, while still performing fairly well at filtering particles. But if thick fabrics aren’t available to you, the study’s data showed that 100% cotton T-shirts, layered up, are also still effective options for homemade masks. (More on this below.)
In general, natural materials are a better option than synthetic ones. Because synthetic fibers (like polyester) tend to be smooth, they don’t filter out particles as well as the rougher texture of natural fibers (like 100% cotton).
What happens when you use multiple layers of a material?
Many DIY face masks incorporate at least two layers of fabric, and sometimes up to 16 or even 32 layers if you’re making multiple folds. So how does that increase the material’s effectiveness?
Testing in this study was done on one and two layers. Robertson told HuffPost, “Doubling the layers increased 0.3 micron efficiency from 2% to 15%, whilst also reducing breathability. It’s difficult to give an exact ‘formula’ for each material on how doubling layers increases effectiveness, as air resistance plays a major part. We want to work on this though.”
Robertson said Smart Air plans to continue its research and release a third edition of the study with more information on layering the materials.
Best materials for blocking large-size particles
The majority of materials tested in Smart Air’s study blocked more than 50% of 1-micron particles, but some of the worst-scoring materials were the wool scarf, bandana (100% cotton) and light scarf (keep in mind, these were each tested in a single layer ― increasing layers slightly increases how many particles can be blocked).
