[I originally wrote this in January 2023 in a social media post. I decided to repost it here. As of September 2025 I’m still very happy with the 3M Aura masks described below.]
Throughout the pandemic, I’ve wondered how effective the face masks I wear actually are.
In medical situations you’re supposed to do “fit tests” to assess how well the mask fits you. The best filtration is no good if it doesn’t fit your face and it leaks around the edges.
Well-fitting is more important than the degree of filtration. That’s why my “go-to” mask so far has been a non-accredited one supplemented by a 3D printed “mask brace” customised to my face to seal the edges.
Recently I read about ways to do a Fit Test at home on a budget. (Fit Test kits usually cost £180 – £500. The gold standard ones use machines costing £10,000.)
I spent £33.39 on the bits to do the home test – and I still have supplies to do tests on dozens of people.
The general idea is you use a bitter solution that’s nebulised into a vapour of droplets. You can taste but not smell it. You wear the mask and put your head into a hood and add the vapour, and then do various tests while breathing through your mouth, to see if you can taste it.
I bought the genuine 3M bitter Fit Test solution, which was the most expensive part. I bought a cheap “facial mister” off Amazon to vaporise the solution. And used a plastic bag instead of a £60 vinyl hood.
The tests worked really well.
Instructions
Here are some references to fit-testing procedures that I adapted for my tests:
The original instructions were on a Twitter thread [broken link, no archive found] by @__philipn__ (Philip Neustrom), which has now been deleted. However they seemed to then make a fit-testing kit – previously sold here. That’s now out-of-stock. But this video reviewed the kit and showed how it’s used.
The official way of using the 3M solution is documented here.
I also got advice from this Reddit thread.
Process
The masks:
The kit. The chocolate is the official way to remove the bitter taste in between each test!
Vaporising test:
Doing a test:
Results
Here are my results (these don’t say anything about the masks, just about how well the masks work for me):
3M Aura 9330+ FFP3
This is always very highly recommended if it fits you. It’s very comfortable on me, but always felt a little loose. I’m pleased to say it passed all the fit tests on me, even the extreme “grimace test”. This will now be my “go-to” mask 🙂
Airpop Light SE, with personalised mask brace
This was my “go-to” combination. It feels very tight and safe, but a bit wearing after many hours. It passed all the main tests. The grimace test leaked, but it popped back into place afterwards. So a decent result.
Airpop Light SE, on it’s own
Immediate fail. Hardly surprising, as it’s not rated to any standard, and only has ear loops.
TGL FFP3
Immediate fail. I’ve never used these, except in emergencies, as they never felt like they fitted me particularly well.
Moldex 3408 Air Plus FFP3
Tentative pass. This is a valved elastomeric respirator. After a few tests, I felt a slight tingling on my tongue. From the level of leakage this suggests 99%+ filtration, so is arguably a pass. Grimace test passed. I wonder if the valve is to blame, as it could let a little air in as it closes on the inward breath.
GVS Elipse SPR299 P3
Also a valved elastomeric respirator, same result as the Moldex. Grimace test leaked slightly but recovered.
Final results
I’m now sceptical about valved respirators being great for self-protection. Still very high protection, but an unvalved one may be better (and they also protect other people from you).
The 3M Aura FFP3 is a brilliant mask, and will be my default from now on. It passed all the tests (for me), even the extreme grimace test. It folds flat-ish to go in a pocket. It’s comfortable. It doesn’t look too outlandish. It’s not too bad for steaming up my glasses (and I also learned that steaming up doesn’t necessarily mean leaks – the filtered hot air coming through the mask can also steam up your glasses). They cost about £4 each and can be reused for a while.
