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30 Oct 2020

Which? face mask tests reveal huge differences in filtration

First consumer test of reusable face coverings reveals some can filter 99% of particles, while others manage just 7%

Our first independent lab test of reusable face coverings has revealed that some cloth masks are highly effective at blocking particles, but that basic single-layer masks may not be up to the job.

We tested 15 reusable fabric face coverings of different designs - including pleated, moulded, stretchy and multi-layer options - to find out how well they filter bacterial particles.

We also assessed how breathable and comfortable they were to wear, and if they survive multiple washes and wears without degrading.

The two top-rated face coverings, from NEQI and Bags of Ethics (both £15 for a pack of three), combined effective filtration with a comfortable and breathable fit. Meanwhile, the £2 Step Ahead mask is an excellent option for those on a strict budget. It's slightly less highly rated than our top-scorers, but still scores four stars out of five for filtration.

Three face coverings were so poor at filtration that we've named them Don't Buys to avoid.

These include the Termin8 face covering (sold in Lloyds Pharmacy and WHSmith) and Etiquette face covering (sold in Superdrug), and the Asda White Patterned face mask. All are single-layer stretchy fabric masks.

We shared our results with the manufacturers / retailers of these face masks. Termin8 and Superdrug (the retailer of the Etiquette mask) disputed our findings and said that their masks conform to government guidelines for fabric face coverings which don't require them to have bacterial filtration. Asda has pulled its face covering from sale as a result of our findings.

See our face mask reviews for the full results and where to buy our top-rated masks.

More layers make for better filtration

The face coverings that performed best in our filtration tests were able to block more than 99% of bacterial particles penetrating the mask material, while the worst managed a paltry 7%.

Masks with several layers proved miles better than single-layer masks at filtering particles. Three-layer masks generally did the best.

Masks which included disposable filter inserts as the middle layer were most effective. They all blocked more than 95% of particles - equivalent to surgical-style disposable face masks.

But one reusable mask, the Smart Mask - sold online, managed this feat without the aid of a disposable filter (which has ongoing cost implications and creates more waste).

What is 'bacterial filtration efficiency'?

This is the standard test used to measure the effectiveness of disposable surgical masks at blocking particles. Coronavirus particles can be much smaller than bacterial particles (as little as 0.1 micrometre in diameter). Face coverings aren't intended to block all particles down to these ultra-fine particles, but instead to help capture larger droplets and aerosols that the wearer breathes out, which can carry the virus. Collectively, this reduction in particles escaping is thought to reduce the risk of community transmission in enclosed public spaces.

Filtration vs breathability

Some of the most effective masks for filtration fell down on breathability. Getting this balance right is key to making a good reusable face covering.

In our tests, face coverings with a poor filtration score were penalised more heavily (as this is their key function), but we looked for a balance of effective filtration and breathability in our Best Buys, for a face mask you won't quickly tire of using.

If a face covering isn't breathable, it can get damp more quickly with condensation, which reduces effectiveness and might encourage people to fiddle around with the mask or take it off.

It's worth noting that, while some masks were more breathable than others, none were seriously difficult to get air through. So, if you are willing to sacrifice some level of comfort for higher filtration, you could opt for one of the less breathable options.

See full breakdown of our face mask test results.

Washing impacts the effectiveness of face coverings

Interestingly, while you might expect your face covering to suffer slightly after a few washes, we found the opposite is true.

Almost all of the face coverings we tested proved more effective at filtering particles after five hot washes, due to the fibres compressing. In fact, there's one mask from ASOS that we think you should wash before using it because of the difference it makes to its effectiveness.

This shrinkage effect was at a micro level, and none of the masks we tested shrunk so much in the wash that it affected the fit, although some became slightly less breathable.

However, bear in mind that over a longer period of time it's possible the fabric will wear and become slightly less effective. So if your mask is starting to look worn out it's time to replace it.

Homemade masks work well, but watch out for the fit

A homemade mask made with tightly woven cotton is an effective option, if you prefer to make your own mask.

We put the UK government's simple homemade face covering pattern to the test, to see how it fared against shop-bought versions.

It filtered 73% of particles before washing and an impressive 81% after five washes - and was still easy to breathe through.

But if you're making your own, look for another pattern: this face covering was let down by a sloppy fit and our testers didn't find it comfortable to wear.

Find out more in our guide to making your own face covering.

Many mask brands fall down on usage instructions

We found the quality of instructions and advice on the face coverings was generally quite poor. Only a few products had clear and easy-to-follow guidance on wearing and washing the face covering.

Concerningly, six of them didn't state that reusable face coverings are not medical devices and seven did not explain how to safely use the mask - both of which are required by (voluntary) product standards.

It's important to follow guidance on correctly wearing, removing and washing your face covering, as wearing or washing it incorrectly could actually increase your risk of infection.See ourface covering usage guidefor more.

Best face masks and coverings for glasses wearers

One of our testers rated each mask for how comfortable it was to wear with glasses and whether their glasses steamed up while wearing it.

The results go some way to proving the annoying reality most glasses-wearers are familiar with: many masks don't get along with spectacles.

The ASOS and AB Mask were the only two that avoided glasses steaming up and were rated highest for glasses-wearers' comfort, with the full five stars each.

The Delphis and Smart Mask were both rated four stars, but unfortunately for glasses-wearers the majority fell below that.

Face coverings latest: when and where do you need a face covering?

Which? reusable face covering tests

The 15 face coverings we tested span a range of designs with different numbers of layers, materials and designs, and are all relatively widely available (at time of writing). We had to omit some big brands due to availability issues.

We chose to focus on reusable face coverings as these are recommended by the UK government and more sustainable and practical for everyday use by the general public than disposable surgical masks.

There is also currently little independent insight into which are best, and no formal standards in place.

Video guide: how we test face coverings

To measure bacterial filtration (how effective a mask is at blocking particles in the air you exhale), we used an aerosol generator to shoot bacterial particles at sections of mask fabric and see what percentage made it through the mask.

We then measured the pressure required to draw air through each of the coverings at a rate of eight litres per minute (slightly above average breathing levels) to see how easy they were to breathe through.

To find out how well the masks would last with repeated use, our testers put on and took off each mask 80 times.

We also assessed how comfortable the face coverings were and how well they fitted, asking three testers with different face shapes to try them on and rate them for comfort, fit and ease of adjustment.

Finally, we washed each mask five times, according to manufacturer instructions, and then repeated all the filtration and breathability tests, and checked for shrinkage or damage.

Face mask tests around the world: what are other countries doing?

Consumer organisations across the world have been doing their own tests of face masks and face coverings. We are working with them to share findings and make this information available to all.

Here are some of the latest findings from our partner organisations across Europe:

  • Denmark Forbrugerradet Taenk tested both fabric and surgical masks, and found a similar inverse relationship between filtration and breathability to us. One of the fabric masks it tested did as well as the surgical masks on filtration.
  • France UFC-Que Choisir tested homemade masks made with different household fabrics such as cotton T-shirts. They found that cotton filtered well and a Kleenex tissue even passed the filtration tests, so could be used in a fabric mask as a disposable filter.
  • Italy Altroconsumo tested reusable fabric masks and found that they were mostly good at filtration - mainly between 80% and 90%. But the breathability scores were much wider and some scored very low.
  • Portugal Deco Proteste tested reusable community face coverings. Most of the masks it tested did well on filtration, but it found larger differences in breathability. It found that 'low levels of breathability compromises comfort and requires more frequent replacement of the mask, because it gets wet faster'.

Consumer tests show reusable masks are a viable option, but there is room for improvement

Our tests, and those around the world, show that reusable fabric masks can be an effective alternative to disposable options for the general public.

But there is a lot of variation, and issues such as compatibility with glasses and clear usage instructions need to be improved.

We're calling on manufacturers to step up and work on improved designs, based on the results of our research.

Disposable vs reusable face masks

Surgical masks are single-use, non-recyclable products, so they're not really a practical solution for sustained daily use and could have a grave impact on the environment.

They're also not the most economical option: at around 45p per mask, the cost of using just one per day over the course of a year would cost you £164.

Both of our Best Buy face coverings come in packs of three for £15, so at £5 a mask that you can use multiple times, it pays for itself in just under two weeks compared with a disposable.

The World Health Organization (WHO) recommends that people over the age of 60 consider using medical masks for increased filtration, especially in high risk areas, but our tests uncovered some reusable masks with a similar level of bacterial filtration efficiency.

How to choose a reusable face covering

  • Try to go for three layers, but at least two - our tests showed a clear difference between single-layer face coverings and those with a double or triple layer.
  • Choose your material wisely. Tightly woven cotton is a good option as the homemade mask we tested did well on filtration - and the worst-performing masks were a single layer of mostly polyester. Ideally, a mix of different fabrics such as cotton, polypropylene and different types of polyester is good.
  • Make sure it's adjustable or comes in different sizes - our testers rated face coverings higher for fit and comfort when they were adjustable, either by the ear loops and mouldable nose wire or because the mask came in different sizes.

Find out more in our face mask buying guide.

*Product testing and scientific analysis led by Matt Stevens, Kamisha Darroux and Sophie Katanchian