I've switched to styrofoam because of that reason and that foil is expensive O.o I use UniHeat as well. I like 72 hours because they last for a long time (I had one last 5 days) and they don't get super hot.
Who am I? Well I am a Junior Member of the International Betta Congress and a breeder of white HMPKs, red dragon HMPKs, black/red dragon HMPKs, metallic multi HMPKs, blue masked HMPKs, and now multi color HMs. Soon to add black HMs. I will be showing in New Breeder class in fall of 2012.