It's just el-cheapo Walmart batting. They carry a couple brands, but I opted for the cheapest which was the Morning Glory brand (High Loft). In all, it's 100% polyester and weighs about 2.7oz a square yard for every 1/2" of thickness. You purchase the rolls of insulation by bed size, so a king size roll ($10.97) measures about 110"x110" and weighs in at 25.4oz. It's not the lightest, but it does work <img src="/forums/images/graemlins/smirk.gif" alt="" />.