we are actually using tagboard at ths first line of defense on our window during this summer, fits snug and I can remove it at night when mornings are cool. In addition, we use stryofoam pannels that face the inside. The third line of defense is desert foil pannels and they are currently on windows that we never open, that foil is on the outside, snug with desert textile window covers. When mornings low are 85, we then tape foil pads to the only window that offer sunlight and will no longer be open.