I just use fabric, usually the fake leather stuff from local fabric store.* I attach the fabric to the 3/4" thermal poly that I have around the 2 sides and back of tank. In WI, I have my house heated 8 to 9 months of the year. So when I have the tank heaters going, I need to keep the heat inside the tanks as much as possible. It really does help keep tank temps more even too. = I know, I'm off topic again.......oh well. 
