Skip to content


The temperature factor, called fRsi factor, is a criterion for the risk of mould growth with a wall connection (connection of a window to the adjoining wall) and is based on DIN 4108-2.

Our video about the tools FEM heat flow results L2D in WinIso®

The factor should reach at least 0.70 so that no mould can develop under standard conditions.

The fRsi value is determined at the point of the minimum surface temperature.