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Study finds multiple layers of coffee filters do filter COVID-19 virus

Researchers studied the effectiveness of one, two and three layers of coffee filters.

PORTLAND, Ore. — Search YouTube, you'll find all sorts of creative, and pretty impressive videos on how to make a face mask out of a coffee filter.

It makes sense. It is a filter. But just how effective is it in filtering out those tiny coronavirus particles?

It was a question researchers at Virginia Tech University wanted to answer. They conducted a study looking at the effectiveness of one, two and three layers of coffee filters.

Dr. Richard Corsi, an air quality expert at Portland State University, followed the research.

"They showed coffee filters can have some benefit," he said.

Keep in mind this was a single study done back in April of 2020. It concluded that the effectiveness depended on how many layers were used.

One or two coffee filters didn't show much benefit, however three did.

"If you put three coffee filters layered on top of each other, you can get on the order of 50, 60 or even 70 percent removal efficiency for particles the size that we care about for the coronavirus," said Corsi.

But the professor pointed out, while three layers does better at filtering out the virus, they also make it tougher to breathe. And air will always find the path of least resistance.

"If it's hard for you to breathe through the filters, it's harder for air to get through the filters," he said. "And air will find those creases around your nose and openings and leakage points around the mask."

Corsi said one trick to sealing up any openings in your mask is by using good old fashioned tape.

"Tape up the creases and it stays sealed for a pretty long period of time if you do it right," said Corsi. "You have to make sure your mask has a good fit and it's breathable at the same time with these multiple layers... it's a bit of an art in the science."

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