In an effort to get as many face masks looped around peoples’ ears as possible, the DIY crowd began work sewing protective gear.

While these cloth versions are potentially helpful in preventing the spread of the coronavirus, there’s a simple “hack” to make them even more effective.

According to researchers at the Missouri University Institute of Science and Technology, adding three layers of coffee filters will do the trick in stopping 24% of particles.

If your mask doesn’t have an interior pocket, a bandana can still work in a pinch, but try to fold in that filter too.

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