Anytime I have done the potato bag thing I have made certain it was sopping wet before putting in my potato. I use just plain muslin, untreated. They still don't come out the same as when as kids we wrapped them in foil and poked holes in the fireplace ashes and buried our potatoes until they were done --had to watch for the occasional exploding one if we hadn't poked the potatoes to break the skins. LOL