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.
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).
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.
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.
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.
A homemade mask made with tightly woven cotton is an effective option, if you prefer to make your own mask.
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.
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.
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.
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.
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.
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:
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.
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.
*Product testing and scientific analysis led by Matt Stevens, Kamisha Darroux and Sophie Katanchian