i should of done more research or gave some resources to what im about to say, but I remember hearing that THC helps out your cellicus(sp?) which help clean out your lungs, cigg smoke does the opposite. What I'm saying is that a pillow case/paper towel cannot clean itself, to be fair, so your estimate wont be exactly like what you see in a pillow case (compared to your lungs) x how long you've been smoking.