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What is thermal resistance (R)? What is more important in the choice of insulation material - the thermal conductivity coefficient or thermal resistance?

Thermal resistance R is characterizes the material of a certain thickness. The higher the value of thermal resistance, the better the insulation. R is expressed in [m2K / W].

Thermal resistance R is the inverse of the coefficient U (R = 1: U); For a wall with a coefficient U = 0.2, the resistance R will therefore be 5.0. The value of the R factor depends on how fast the heat will escape from a home. Unlike the thermal conductivity coefficient and the heat transfer coefficient, the higher the thermal resistance, the better.

Heat resistance is the ratio between the thickness of the material layer and the thermal conductivity of the given material layer.Ri = di/λi

Where:

Ri – thermal resistance of material layer [m2K/W],

di – thickness of material layer [m],

λi – thermal conductivity coefficient [W/mK].

This implies that the better (lower) lambda and the greater the material thickness, the better the thermal resistance of the layer.

Example:

 Heat resistance for a 12 cm thick material with a thermal conductivity λ=0,039 W/mK wynosi 3,08 m2K/W.

Heat resistance for 12 cm thick insulation with a thermal conductivity 0,024 W/mK is much higher and is 5,0 m2K/W