Zoo Meds Repticare Rock Heaters are made of a hydrated rock material that is twice as strong as cement or pumice, resulting in excellent conductivity and increased product longevity. Hot spots are not a problem with a completely encapsulated full coverage nichrome heating element that distributes heat evenly. Zoo Meds Deluxe Repticare Rock Heater features a rheostat control allowing you the ability to adjust the surface temperature. Additional Information: Please Note: A rock heaters function is to facilitate digestion. A rock heater should never be the sole source of heat unless the ambient air temperatures in the cage are sufficient for your type of reptile. Zoo Med rock heaters are cUL/CSA/T1/2V approved