Flexatt allowed to heat uncontrolled will reach temperatures far beyond it's intended use. That's the reason why almost all reptile thermostats won't run higher than 110 degrees. When you have a heating element such as flexwatt that is taped to a surface, it can't breath and all the heat put off will generate more heat. When he temps reach a certain point, the plastic casing around the actual heating element of the flexwatt will begin to burn thus potentially causing a fire. Flexwatt is desingned to provide a hot spot not heat an entire enclosure.