The advantage of the three-chamber system for PE 68 windows is a high level of insulation, achieved when using special isolation cases. The heat transfer coefficient (for frame) of PE 68 with closed chamber is Uf=1.5 W/m2K, while the heat transfer coefficient of PE 68HI windows with higher thermal insulation is 1.3 W/m2k. It is usually used in buildings to achieve better energy efficiency.