A thermal bridge is a specific or linear area of ​​the building envelope, in which heat is transmitted more easily than in the surrounding areas, due to a variation in thermal resistance. This is a place where the insulating surface is broken.

Thus, a thermal bridge appears due to.

Before thermal insulation of buildings became widespread, bridges represented between 10 and 20% of total heat losses. Later, when more care was taken of the insulation, the percentage of losses due to flat elements decreased greatly, while that of the bridges increased significantly. Currently, regulations require reducing the energy demand and consumption of buildings, such as the European directive on the energy efficiency of buildings[1]​ which requires construction solutions to reduce losses due to thermal bridges to a minimum.

A simple example of a point thermal bridge could be a screw that joins two sheets of wood. Since the screw conducts heat better than the wood, more heat escapes through the screw than through the wood. For this reason, avoiding, or reducing, thermal bridges is essential if you want to reduce heat losses.

Thermal bridges can be in the enclosure itself, such as pillars, openings and blinds. Also between different enclosures: forged-facade, roof "Cover (construction)")-facade, foundation-facade, interior partition-facade.

A common case is that of insulating glass windows with an aluminum frame. Insulating glass has lower conductivity than the aluminum frame, and therefore heat losses through the frame are greater. In winter you can see sweat (small drops of condensed water "Condensation (change of state)") on the frames) without said condensation occurring on the glass.

To avoid this heat transmission, what is called thermal bridge break is used. It consists of preventing the inner and outer faces from coming into contact with each other, inserting a poor conductor, thereby reducing heat losses. In the case of laminated profiles, they must include double lamination, one exterior and one interior; The space or vacuum generated between the metals will serve as a temperature dissipator.