Thermal insulation properties
Finnfoam's thermal conductivity
|Nominal thickness||20...30 mm||40...60 mm||70...120 mm||Finnfoam F-29, 160-400mm|
The U-value, calculated from the thermal conduction properties of the materials, rarely tells the whole story of a structure's insulation capacity. The structural air leak value (n50) also affects the structure's insulation capability considerably. The tighter the structure, the better its thermal insulation capacity. Finnfoam's cell structure is completely homogenous and sealed. The U-value does not address internal convection occurring within the structure, which increases as temperature difference grows. Finnfoam is not subject to internal convection, however.
Finnfoam's thermal insulation capacity is almost completely independent of the conditions of use. The completely homogenous and closed cell structure retains the clean air used as a cell gas very efficiently. Its thermal conductivity (λ10) is 0.026 W/(m K).
Air flow does not weaken the material's insulation capacity. This is why it can also be used as wind protection. Finnfoam's heat conductivity (λ10) is 0.029–0.034 (W/(m K), depending on the board type. As the material is impermeable to water, it also retains its insulation characteristics in humid conditions. This is a very important property for ground frost insulation materials.
Structures insulated with Finnfoam require no separate wind protection. For reasons of moisture management and elimination, however, Finnfoam cannot be used as a wind protection sheet in, for example, insulation wool walls.
As Finnfoam's cell gas is air, its insulation capability does not deteriorate over time. As the heat conductivity of air decreases as the temperature falls, Finnfoam's insulation capacity increases in cold conditions and the best insulation capacity is reached in very low temperatures. The temperature value used as the dimensioning specification for ground frost insulation is -5°C. At this temperature, Finnfoam's insulation capability is already increased. As water does not permeate Finnfoam, the material's thermal conductivity value used for dimensioning purposes, according to the present CE and European standard specifications, is even better when exposed to humidity (0.034 or 0.036, compared with 0.035 or 0.037 for dry applications). In dry applications, the thermal conductivity value used for dimensioning is usually equal to the declared lambda value. As Finnfoam is also airproof, air flows do not have a negative impact on the material and, as the cell gas is air, no deterioration of thermal conductivity occurs over time.