I have an old Campmor versatile tarp that has started to lose the polyurethane coating. I ran it through the washing machine to see what would happen and big chunks of the coating came off. If you look at the how to's for McNett Gear Aid Tent Sure repair coating, they recommend a mix of water, Isopropyl Alcohol and detergent to remove the old coating. It would appear that polyurethane coatings do not respond well to washing. I don't know that any of this applies to silnylon or silpoly.