This is the source text for a printout to give out to people participating in community fit testing.

What is fit testing?

Fit testing is a way to see how well your masks work for you. While most high quality masks are made out of material that filters around 99% or more, the seal to the face makes the biggest difference in how protected someone is.

The kind of fit testing we do is called “quantitative fit testing.” There is another kind of fit testing called qualitative fit testing where someone tastes an agent that's aerosolized in the air.

What does a fit test tell me?

With the kind of test we do, passing a fit test means you’re probably getting around 99% or better when wearing your mask.

Without a fit test, most people can get around 90% when wearing a N95 with headbands when clean shaven and going with their intuition. With earloop style masks (KN95, KF94) this number is lower. And many people do not necessarily get to this 90% level in even an N95.

A fit test tells us you are very likely in the 99% or higher range. We will give you the exact 'score' you get when doing the test which can be used to guess at the exact % filtration you will be getting when wearing your masks.

What are the limitations of this testing?

The biggest limitation is that you may put on your mask in a slightly different way next time you wear it. Because we only test once, this means you could have a subtle difference that affects fit.

A good example of this is facial hair. If you have facial hair and allow it to grow out for more than a day, you will likely not get as good of a fit.

We working to make materials for home fit testing more available. If you have a home testing setup you can test a few times with each mask you wear to have a good idea of how consistent your fit is.

Does passing the fit test mean I can’t get COVID when wearing my mask?

No. Fit testing is a risk reduction measure and is not a guarantee.

I passed on several masks but I got a higher score on some masks. Are the masks with a higher score safer?

Yes. But we don't know what filtration level is needed for a given situation. In workplace settings where people are required to wear fit-tested respirators, a "fit factor" of 100, or roughly 99%, is deemed as acceptable.

But the higher the score, the more protective the mask is. There is also a "margin of error" in these tests so minor differences may not matter. Your fit tester should explain this when giving your results.

I have a mask at home that’s really cool and has P100 filters but I didn’t fit test it, is it better than the masks I fit tested?

Your fit tested masks are likely more protective than your non-fit tested masks, even if your non-fit tested masks have higher filtration or are elastomeric respirators.

Is the test we did an official OSHA fit test?

It's very close, but there are some differences. The tests we do not not technically qualify as an OSHA fit test. We are using an older machine that hasn't had been calibrated by the manufacturer and the OSHA specification states that regular manufacturer calibration is required. Depending on how your fit tests were performed, they may have been done outside rather than inside which may have some effect on the exact score your masks get.

How can I get more information about home and community fit testing?

We’re sharing resources on our twitter account: