U-value & K-value
To indicate to what extent a material is thermally insulating, the term thermal transmittance or U-value (formerly known as K-value) is used in the construction industry. The lower the U-value, the higher the heat resistance of a material, meaning the better the insulation.
For an optimal match between profiles and glazing you should take into consideration the U-value of both. Reynaers systems answer to the requirements of the European directives as well as various international standards on energy performance.