Mechanical science and engineering professor Taher Saif spoke with News Bureau physical sciences editor Lois Yoksoulian about a study that he and his graduate students, Onur Aydin and Bashar Emon, performed on the effectiveness of common household fabrics for use in homemade masks.
Physically speaking, are the respiratory droplets produced by talking and breathing the same as those that come from a cough or a sneeze?
The droplets released during sneezing and coughing are larger than those released while speaking and breathing, and any of these droplets may carry many virus particles. The larger droplets tend to fall nearby due to gravity, but the smaller ones can go far, with the majority of them remaining within six feet of the infected individual. Unfortunately, because symptomatic, presymptomatic and asymptomatic carriers can shed the coronavirus, we cannot tell without testing which individuals are the sources of infection. Hence, a physical barrier, such as a mask, can prevent the spreading.
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First, most common household fabrics, such as T-shirt material, have 40% or higher droplet blocking when used as a single layer. In two layers, to our surprise, T-shirt fabric had a 98% droplet blocking efficiency – exceeding that of the medical mask, while maintaining better breathability.
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What type of fabric do you recommend for the home mask maker?
We found that very breathable fabrics are a good choice, like common t-shirt materials. They tend to have low droplet resistance, and their efficiency increases when used in a two-layer mask. The net breathability of the two layers is much higher than the medical masks, too. In fact, the breathability of cotton T-shirt fabrics remains higher than a medical mask, even with three layers.
