In camping, a ground pad, sleeping pad, thermal pad, sleeping mat, or roll mat is lightweight pad, common among hikers, backpackers and budget travelers, often used in conjunction with a sleeping bag. Its purpose is to provide padding and thermal insulation. All types currently available use air as their primary form of insulation.
In its simplest form a sleeping pad consists of a foam-like material that is about half a centimeter 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.
A common misconception is that the pads are primarily for creating a more comfortable sleeping or sitting area. Instead, the primary purpose of the pad is to prevent the loss of body heat into the ground while sleeping. The materials used are typically filled with air pockets, slowing down the conduction of heat through the pad, as air is one of the best (and cheapest) insulators.