GlaxoSmithKline (GSK) is one of the biggest pharmaceutical companies with branches all over the world. In winter there department in Marly-Le-Roi France suffered severe heat losses trough the windows. In consequence of this, they decided at GlaxoSmithKline in Marly-le-Roi to install Umisol® window films. The Umisol® window films were installed on double glazing with U-value of 2,9. The tests proved that there is a significant improvement of the internal isolation in winter, with an increase of the average temperature with 3,5°C.