painting Respirators (single stage Urethane-BCCC ) what are you using ?

Here is a decent deal on the cartridges I've used. My understanding is the activated carbon portion of the cartridge begins absorbing airborne particles and moisture as soon as the package is opened, so they have a limited useful life once opened even if they're not actively being used. Storing them in a sealed ziplock may extend their useful life. For the limited amount of painting I do, I just use a fresh set for every project.

3M OV P100 Replacement Cartridges for Household Multi-Purpose Reusable Respirator (1-Pair) 60921HB1-A - The Home Depot