Vacuum cleaner bags make best face masks

Reusable sacks effective at trapping airborne particles while also letting users breathe, say scientists

REUSABLE vacuum cleaner bags are the best material from which to make homemade face masks, the University of Cambridge has concluded.

The cloth bags, which can be cleaned in a washing machine, were found to be the best at preventing droplets and aerosols from escaping, while still allowing wearers to breathe sufficiently well.

Although some materials, such as thick denim and polyester were better at stopping the spread of ultrafine airborne particles, they made breathing too difficult to be useful.

“A mask which blocks particles really well but restricts your breathing isn’t an effective mask,” said author Eugenia O’kelly of Cambridge’s Department of Engineering. “Denim, for example, was quite effective at blocking particles, but it’s difficult to breathe through, so it’s probably not a good idea to make a mask out of an old pair of jeans.”

While there are numerous online patterns that help people make their own masks, there is little scientific evidence on what the most suitable materials are.

Researchers placed a fabric sample between two sections of tubing and sent through tiny aerosolised particles at high speeds, comparable to someone coughing or breathing heavily.

Wearers were asked to comment on how well they could breathe through each fabric to give an overall score.

Polyester “windbreaker” material, used for outdoor jackets, was highly effective but graded in the worst category for breathability. Denim was also good but difficult to breathe through.

A folded sock was as easy to breathe through as a vacuum bag, but not as effective at catching particles. Likewise, lightweight T-shirt material was easy to breathe through yet only stopped around 10 per cent of particles. In contrast, reusable vacuum cloth bags caught more than 40 per cent.

For homemade masks those made of multiple layers of fabric were more effective, and those which incorporated interfacing – normally used by tailors to stiffen collars – were found to stop up to 60 per cent of particles.

However, more layers also made them more difficult to breathe through.

Ahead of the study, the researchers consulted with online sewing communities to find out what types of fabric they were using to make masks.

Due to the severe shortage of proper filters at the time, several of the sewers reported that they were experimenting with inserting vacuum bags.

Although researchers found that both single-use and reusable vacuum bags were effective at blocking particles, they cautioned that single-use bags should not be used in face masks, as they fall apart when cut, and may contain component materials which are unsafe to inhale.

They also studied the performance of fabrics when damp, and after they had been through a normal washing and drying cycle. They found the fabrics worked well while damp and worked sufficiently after one laundry cycle. However, previous studies have shown that repeated washing degrades the fabrics, and researchers cautioned that masks should not be reused indefinitely.

The results were reported in the journal BMJ Open.