Thermal bridge

A thermal bridge or thermal bypass is any thermally conductive material in an otherwise insulated wall that allows heat or cold to quickly penetrate the wall. For example, a wall insulated with XPS foam board, but which has metal ribs between the foam, has a significant thermal bridge. Any conductive material that penetrates the insulation can be a thermal bridge. This includes metal fasteners, structural beams, etc. Junctions of different materials can also form thermal bridges, such as a wall to ceiling connection.