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. 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.