I backed https://purme.co/mask/ because when I am doing things like sanding, or laser cutting, or emptying my dyson, I haven't been able to find a mask with a decent fit. And I thought flexible silicone mask sounds like a good idea. Works for scuba diving.

The main issue I have is that the filters are not very well supported and a deep breath in can warp the filter disk, leaving a gap.

This is a simple support to keep the filter from warping when you take in a deep breath.