thoroughly. I noticed when I took my filter outdoors to blow dust out of it I couldn't see much sunlight shining thru the paper. Took it to the shower w/ the shower head on a hose and washed it w/ the pulsating spray until the water running off it cleared up. Set it on a furnace vent overnite and can now see sunlight thru the paper. It doesn't seem to have suffered any damage from the ordeal and it if works as good as new has saved me about $30. Just thought I'd pass this along.