They claim to be unbreakable and you know what I don't see that happening under normal circumstances even if you get a bit rough with them. There's no Glass so nothing to crack when they overheat, not that they can overheat anyway. This device is equipped with a safety thermal switch that stops operation if it's out of water. Modern plastic heater with thermoregulation. Absolutely Unbreakable Wide range of precise regulation Fully submersible (IP68 Standard) Overheating switch control Easy to install and service.