Three-Dimensional Activated Carbon Filters 5 Layers Replaceable Filters Paper,5-Layer Anti-Fog (30)

I love how these fit the mask, filtering out all the air you breathe in. I'm using them in all my masks, and have shown them to others, who are now using them too.They are a little fiddley to get in, but once they are inserted in the filter pocket, they work quite well.

Their layers and thickness seem much more effective than the light weight flimsy ones. They are stiff enough to stay in place well.