Reusable face masks are now an essential household item, but it seems not all are created equal. A study by consumer champion Which? found huge differences in the effectiveness of widely-available reusable masks. 

The study revealed some of the best performing face coverings are able to block more than 99% of potentially harmful bacterial particles, but found the worst allowed up to 93% of those particles to escape. Not great.

It’s worth noting straight off the bat that face covers are not the same as surgical face masks – and are sold with the caveat that they’re not medical masks.

But fabric face coverings are intended to help block larger droplets and aerosols breathed out by the wearer. Which? tested for factors such as: how well a mask filters bacteria, how breathable it is, and how it fares after multiple washes.

Here’s what they found.

The ‘worst’ face masks

Three out of the 15 face coverings Which? tested performed so badly they were deemed a ‘Don’t Buy’.

At the bottom of the table and earning the lowest scores overall were a face covering from Termini8 sold at Lloyds Pharmacy (£2), one from Asda (£3) which is no longer on sale, and one from Etiquette (£3), which is sold at Superdrug.

All were lightweight and breathable as they were made with only one layer of material, but this affected their ability to filter potentially harmful particles, earning each mask only one star out of five in this category.

Studies have found three layers is preferable to filter out harmful particles.

A spokesperson for LloydsPharmacy told HuffPost UK it takes the quality and efficacy of the products it sells “very seriously” and that the Termin8 mask is compliant with all necessary requirements as set out by the Department for Health and Social Care and the British Retail Consortium.

“In addition to a range of face coverings we also stock a wide range of face masks that meet medical standards, which have not been included in the Which? testing,” the spokesperson added. 

The Asda mask is no longer on sale – and hasn’t been for some time. A spokesperson added: “Product safety is our key priority and all of our George face coverings comply with and British Retail Consortium guidance and the Office for Product Safety and Standards.”

Superdrug disputed the testing methods used by Which? and said it’s “disappointed” at the Etiquette face cover’s Don’t Buy’ rating. “It has been tested against the EN 14683 standard for surgical masks and the CEN Workshop Agreement which is not an official standard,” said Superdrug’s spokesperson.

“This product was clearly retailed as a fabric face covering and not a surgical mask – designed to help the wearer reduce the spread of a cold or virus, as per government guidelines.”

The ‘best’ face masks

Two of the products tested were awarded Best Buy status: the NEQI reusable face mask (£15 for 3), which is available from retailers including Boots and Ocado, as well as Bags of Ethics Great British Designer face coverings (£15 for 3), available at Asos and John Lewis.

Both were considered comfortably breathable, earning the full five stars in this category without compromising on filtration (four stars out of five).

For the tests, Which? used an aerosol generator to shoot bacterial particles that were 3 micrometers in diameter at sections of mask fabric and see what percentage of bacteria made it through. 

The lab tests revealed that masks with multiple layers are much more effective than single layer masks at filtering particles.

Interestingly, tests revealed that almost all of the face coverings got better at filtering particles after being washed. Face coverings were re-tested after five hot wash cycles, and most improved, due to the fibres compressing. 

Best for glasses wearers

The Asos (£12) and AB Mask (£10), which is available at Boots, were the only two masks that didn’t cause glasses to steam up and were rated highest for glasses-wearers’ comfort, with both scoring five stars in this category.

What now?

Which? is urging manufacturers to use these findings as a basis for improving their products, while retailers should seek to ensure they are selling products that will effectively filter out potentially harmful particles, it said.

In the meantime, Which? is encouraging consumers to research the best available options for themselves and others before making a purchase.

Natalie Hitchins, head of home products and services at Which?, said: “With face coverings now such an important part of daily life, they not only need to be durable and comfortable, but also provide effective filtration from harmful particles in order to keep us and others safe.

“Our results prove that there is a huge difference in quality between reusable masks sold in stores around the country and online. We would urge manufacturers to use our findings to up their game and improve their products – until then it is worth taking time to research the best option for yourself and your loved ones.”