Carpet laying

This is the Oriel window in our bedroom, Looks very nice but is totally impractical. Window cleaning is a balancing act and as the base is a concrete slab about 6 inches thick with a marble window cill when we get cold weather the whole window does a good Impression of a fridge. The house was built in '95 so Insulation is primitive.  After 2 winters we decided to do something, first we bough a cheap rug and cut it to fit, big improvement, then I put 2 cms of Styropor under the carpet, WOWW!! Problem solved! Why didn't I do it before? Still cool in there, but not icey anymore.