Kitchen sink "fit testing" smell/taste/irritant ..... and temperature

If you have a mask that purports to have higher filtering (like my Ragmask Max design - https://cv-masks.github.io/ragmask-max.html) and you want to know how good the fit is so that you're sure there are not leaks, then you'll want to use a machine like a Portacount fit tester.

Of course not everyone has one of those, so smell/taste/irritant test is the classic Mechanism that's more accessible - https://urgentcarementor.com/how-to-conduct-a-respirator-fit-test/

I'm in Scotland and it was 6°C (46° F) a few days ago while I was wearing my 7-layer fabric mask that is otherwise tight on my face. Six of those layers are thinner satin (a good filter), and one is a 400-thread cotton outer. My own exhaled breath is warm, of course, but the outside air is cold by anyone's definition. So when I breathe in and my throat around the lower seal of the mask gets momentarily colder, I'm learning that air is leaking through that seal. Unfiltered air. For other people a mask that is mal-fitting differently might feel colder at a different edge (like around the nose).

Thus my filter is too good (for this mask), and my strong lungs are able to pull air in from wherever they can, which means not going through the 7 layers and instead going around it. Less layers don't have that problem, and to be honest 7 layers (six satin) was showing off.