For months, scientists have been saying that the masks reduce COVID-19 transmission. Now they think that masks can also make the disease less severe.
The reason is that the barrier created by a mask probably limits the amount of virus the user is exposed to. Less viral load can cause less severe symptoms.
Simple cloth masks, the type of face covering recommended to the general public by the Centers for Disease Control and Prevention and the World Health Organization, offer some protection against coronavirus, but can be improved by adding a layer of filter.
First, you need a fabric mask of at least two layers of tightly woven cotton with a pocket into which you can insert a filter. The filter should be at least one layer, two is better, non-woven polypropylene, also known by the brand Oly-fun (Walmart) and spunbond.
We mentioned this type of filter in a previous article about the best and worst options for a fabric mask. But a couple of readers expressed confusion about grams per square meter of weight and fabric measurement for polypropylene.
An easy way to make a polypropylene filter is to cut a square to fit your mask from a reusable cloth shopping bag with the No. 5 recyclable label. These are also the type of bags distributed at conferences. The fabric-like material can be identified by its small diamond-shaped indentations.
The fabric, which is the same material used in the N95 masks, although with a different fabric and thickness, is easy to wash, allowing multiple uses. It has an electrostatic charge that traps both incoming and outgoing particles. After washing, it can be “recharged” by rubbing plastic gloves. Ironing also works.
When you put a filter made of two layers of charged polypropylene in your pocket, the mask’s filtration efficiency could double up to 70%, Yi Cui, a professor of materials science and engineering at Stanford University, told NPR.
What about other materials? Some publications have recommended coffee filters for masks, but breathing through a filter intended to brew your morning coffee is difficult and can cause you to inhale and exhale around the filter rather than through it.
A University of Arizona study published in Science Daily earlier this month found that vacuum bags could be reused as effective mask filters. Various DIY videos on the Internet offer tips on how to make them. However, at least two vacuum cleaner manufacturers, Bissell and Shop-Vac, recommended that people refrain from turning their bags into filters to cover their faces.
If you make a filter with a HEPA (High Efficiency Particulate Air) vacuum bag, do not wash it. Washing weakens the effectiveness of the filter.
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Mike Moffitt is a reporter for SFGATE. Email: [email protected]. Twitter: @Mike_at_SFGate
