Treat the insulation substance as homogeneous, While in true apps, rigid elements have joints and in some cases cracks. Thus, the U-worth is often better than what It could be In the event the insulation behaved for a homogeneous materials. Reference 2 presents steering on calculating U-values. uPVC window and https://ambientindoorlights90011.blog2learn.com/82305698/the-2-minute-rule-for-window-insulation