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Thermal Break. All the truth about Thermal Break (RPT)

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What is exactly the “Break of Thermal Bridge”Rotura de Puente Termico” in Spanish (RPT)? Many have asked that when choosing an aluminium window. Well; Thermal Break is to insert a low conductor material between the external and internal side of the aluminium frame and then join both sides. With this method we make difficult the transmission and the consequent losses of heat, as well as the condensations. Although it is not a very complex concept, maybe for the most curious or sceptic Thermal Break still has some mysteries that we, in Extrual, would like to answer.


 For that, we should consider the physical and structural concepts involved.


Thermal conductivity (λ) and transmittance (U)

Thermal conductivity is the ability that a material has to transfer heat through it. The thermal transmittance is the measure of  the heat that flows through a constructive system. It is opposite to the “thermal resistance”, that related the conductivity and the thickness (density) of the layers which are part of the system.

Thermal Bridge

It occurs a thermal bridge when a specific element (a window frame, for example) has a higher U transmittance value than the adjacent element (the walls). This situation makes that the heat, which always looks for the easiest way out, tends to escape through these elements. In other words, thermal bridges are motorways on which heat can escape at a higher speed.

These images belong to a comparative between aluminium carpentry with and without thermal break. In the first one heat finds a great difficulty to cross the Thermal Break. We can appreciate two faces (sides), one hot (the inside) and a cold one (the outside). However, in the next one the heat distribution is uniform, being the interior of the carpentry at 17ºC.


A derivated effect from termal bridges are condensations. These are produced when the water vapour comes into contact with the thermal bridges, colder, causing its condensation in liquid water. This effect is the responsible for the appearance of moisture and mold.

Given the high conductivity of aluminium, we must insert in the windows and doors profiles an intermediate layer of an insulating material to “break” this thermal bridge. But, how?


 Aluminium profiles with Thermal Break

Thermal Break in aluminium profiles can be obtained by inserting insulating polyamide strips, reinforced with a 25% of glass fibre. This material has a conductivity almost 800 times lower than aluminium (*), establishing a continuous insulating barrier which prevent the heat transmission. Following the previous comparison, the heat finds a very expensive toll that prevents its leak (flow).

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