Thermal pads or ground pads are thin, lightweight pads that are common among hikers, backpackers and budget travelers. In its simplest form a thermal pad consists of a foam-like material that is about half a centimetre thick (about a quarter of an inch). The dimensions of the pad are usually about the same length as a sleeping bag and a little wider. Slight variations in design can be found, such as rippling in the foam, but these do not significantly affect the pad's thermal properties.