Frequently Asked Questions
When we carry out a test on a mask, it is actually two tests at once. We place the mask in our testing equipment and evaluate the fabric’s performance against two parameters. The first is filtration efficiency, and the second is pressure drop, which translates to breathability.
Filtration Efficiency rates how good the fabric the mask is made of at filtering out droplets of a certain size. The droplet size (sometimes called particle size) we use to derive this result is 3 microns, that’s 3 one-thousandths of a millimeter or 3 millionths of a meter. That’s very small. A human hair is about 70 microns wide. If a fabric stops 70% of all droplets at 3 microns or bigger, it is what we consider, along with the European guideline for non-medical face masks, to be the benchmark for good filtration
Our second rating is breathability, which is the inverse of the Pressure Drop we measure across the fabric the mask is made from. The higher the pressure drop, the more difficult to breathe through and the more likely that breath will simply shoot around the edges of the mask instead of through it. We flow Nitrogen though the mask at 7.3 litres per minute, which is slightly above the rate at which a resting adult male breathes. This flow rate was selected as it is representative of the average velocity through a mask. Then we measure how much resistance there is through the fabric. We use 100 Pascals at 96 l/s/m2 as the benchmark.
The purpose of non-medical face masks is to mitigate or lessen the likelihood of virus-laden droplets from being blown around. With fabric technology being where it is today, the better something is at filtering typically means it is worse for breathability and vice versa. If a mask has too much breathability, then it typically means it isn’t good at filtering. For instance, a very breathable mask made from the netting you get oranges from at the grocery store would be great to breathe through but it won’t do much at all to stop tiny droplets from getting through. Similarly, if the fabric a mask was made from was completely solid, such as cling wrap, nothing would get through it, but you wouldn’t be able to breathe in either. What’s worse is when you breathe out, all of your breath would simply go around the mask and not be filtered at all. This is the reason why masks with non-filtered exhaust valves are NOT sold on LabTestedMasks.
One of the most critical aspects of wearing a mask, any mask, is how well it fits. This is why N95 respirators require annual fit-testing to be carried out by a professional and wearers typically cannot have facial hair. Because every face in the world is different, we cannot guarantee the way a mask will fit anyone, so we don’t score the mask itself, we score its fabric. By scoring the fabric only we can ensure that the test results are consistent and repeatable, and you can be confident in what you are buying. We also don’t grade a mask based on how a removable filter performs. This is because filter inserts are typically smaller than the breathable area of the mask itself and have such high pressure drop that exhaled breath may simply go around it rather than through it and could lead to inconsistent results depending on the shape of wearer’s face and how the mask might fit.
Each mask product page features a score for Filtration Efficiency as a percentage and Breathability graded 1 to 5. Read more...
As described above, the filtration score and the breathability score work in opposite directions, so the highest filtration score likely won’t have the highest breathability score, and vice versa. As a result, there is no “best mask” and it is up to each individual to select a mask based on what they value most. You might want a high filtration score for use on public transit, and a higher breathability score for use at the gym, or maybe a balance of the two for running daily errands.