The flimsy masks that are currently available don't really work for sanding dust.
I have a limited stash of N95 masks that I am holding in reserve.
I have an older organic vapor/particulate 3M mask that works fine for spraying and such - but is way too hot for sanding.
I read about the Elipse masks and decided to try one.
Highland Woodworking (among others) sells the Elipse P100 dust mask.
A lot more comfortable than the 3M. The exhalation valve means you can use it
for being around people - but I only wanted it for the shop.
A reasonable, comfortable mask. The medium/large fits me quite well.