Starting with a suggestion from a friend I have used black plastic with double water tubes as a winter pool cover for somewhere around 12-14 years. I started out using store bought pool covers but by year 2 they were shot. A 24'X100' roll gets me through 2 seasons and leaves enough for various home projects. I learned real quick to use only once. Not the "greenest" thing to do. I hope the trash collectors recycle it but the smell may be more than they care for. When I searched on using black plastic I didn't find any other entries. Is there something I'm missing or should I be embarassed to even bring this up. What I want to know is what thickness do others use, typically 4 mil or 6 mil?