The equivalent thermal conductivity has been determined in accordance with the ift guideline WA-17/1 “Thermally improved spacers – Determination of the equivalent thermal conductivity by measurement”. The representative linear heat transfer coefficients calculated in this way (representative Psi values) apply to typical frame profiles and glazing for the determination of the heat transfer coefficient Uw of windows. They have been determined under the boundary conditions (frame profiles, glazing, glass mounting depth, back covering, primary and secondary sealant) defined in the ift guideline WA-08/3 “Thermally improved spacers – Part 1: Determination of the representative Psi value for window frame profiles”. This guideline also governs the area of validity and application of the representative Psi values. In order to avoid rounding errors, the Psi values in the data sheet have been given at 0.001 W/mK. The method for the arithmetical determination of the psi values has an accuracy of ± 0.003 W/mK. Differences of less than 0.005 W/mK are not significant.