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When shopping for masks, you will no doubt see claims that the mask is N95 or N99 rated. What does that actually mean, and how does that relate to PM2.5, which is another number that seems ubiquitous when looking for masks.

What’s the difference between N95 and PM2.5?

The first distinction that needs to be made is that a N95 or N99 label is related to the mask’s ability to filter out airborne particles, whereas PM2.5 refers to the size of the airborne particles themselves. So for example PM2.5 refesr to particles that are 2.5 microns, which is equivalent to 1/3 of the diameter of a strand of hair.

A N95 rating means that the the mask is able to filter out at least 95% of airborne particles larger than 0.3 microns. A N99 rating means that it is able to filter out more than 99% of airbone particles larger than 0.3 microns.

These ratings are U.S. based standards, from the National Institute for Occupational Safety and Health (NIOSH).

I also see ratings like KN95, FFP2 – what are those?

You will also see ratings such as KN95 , P2 and FFP2. These are equivalent standards in other parts of the world, all referring to the same rating as the N95. For example, KN95 is the Chinese standard, P2 is the Australian standard and FFP2 is the European Union standard.

While the exact tests performed under the respective countries and their standards are slightly different, there are generally regarded to be “equivalent”, such that if you purchased a mask with a KN95 or FFP2 rating, it is the same as a N95 rating.

3M has a good comparison of the tests performed by different standard bodies around that world that that are equivalent to the N95 standard.

What is the N95 rating actually on?

It is important to understand what the N95 rating is actually on. For respiratory masks, the N95 rating is on the entire mask itself. They are therefore more effectively at filtering out airborne particles. In our other post comparing the effectiveness of masks on filtering air pollution, respiratory masks routinely scored higher than 97% in filtration performance.

For cycling masks or everyday pollution masks, the N95 rating is on the replaceable filter, not on the entire mask. So while the filter itself is certified to filter out 95% of airbone particles, the overall filtration performance of a cycling mask has been tested to be around 80% as the mask itself does not have as tight a seal as a medical grade respiratory mask.

Does this mean that everyone should go out and buy N95 respiratory masks? Not necessarily. Theses masks are designed for medical and industrial applications, are single use, and are uncomfortable to wear for prolonged periods of time. A washable, reusable mask with replaceable filters can be more practical, presents better value for money over time while providing adequate protection from harmful particles. You could even wear a surgical mask inside a pollution mask to prolong the life of a single use surgical mask while creating an additional layer of protection.

Certification results of our Stride mask filters

The filters for our Stride cycling/sports mask is certified to the KN95 standard. It involved taking 10 samples, and applying a filtration test. The filtration test involves inhalation and exhalation resistance tests, at a flow rate of 85 L/min. This is a laboratory test where specific aerosols (NaCl) are made to pass through the filter.

10 filtration tests were conducted on randomly selected filters from the samples. The result of the tests showed that the filters’ filtration performance was always over 97%, with a high of 97.9%. Therefore our filters actually exceeded the KN95 level, and therefore our certification was successful. Our results are shown below.


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