Some frames have insulation boards inside to keep the structure warmer. Some home gardeners use a portable frame which is not buried so it can be moved or stored. If the sides are not dug into the ground, bank soil around the frame or add insulation boards to conserve heat. A coldframe may also be built as a lean-to against a house or garage. The sashes or top panels can be made of glass, plastic film, fiberglass, plexiglass or other translucent material and can be hinged to the frame or left loose.
Plastic film is economical but can easily tear.
Although more expensive, fiberglass will last many years with proper care. Glass has excellent light transmission qualities but can be dangerous, especially if children play in the area. On a 6' x 6' frame, two 3' x 6' sashes may be used with one sash support arm in the middle of the frame. Screen can be placed over the coldframe to keep rodents and insects out when sashes are removed or vented during warm days. Hotbeds A hotbed is a coldframe built over a heat source.