Flexwatt
All I use is flexwatt. It is a great product but there are precautions that must be observed. If you use flexwatt, it must be regulated with some sort of temperature control device. I run mine vertically on the back of a rack instead of under a glass aquarium. However, it can lay under a stationary aquarium. Don't slide things over it. It will rub a hole in the tape, and that will create a fire hazard.