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.