1 earlier comment mentioned my A/C. If I reach down to the grills, cold air is coming out as it should. Nothing is kinked anywhere. I just can't ask A/C 2 floors above where the pumping starts to overcome 8 hours of direct sun. Now without the 8 hours of sun, it's cool. The issue is about direction. Given the science of the sun, it rises east, moves in an arc across the sky from east to southeast to southwest to west, so that upstairs window facing south has sun beaming through it from about 10am to about 6. That includes the time window including the hottest hours of the day. That room hits 90. When the A/C is set to 68, the main floor is 68, and that one room upstairs is 90, the other room is 85. Since putting that foil up, that room now stays at 75 or less. Without that 8 hours of sun, it never has the chance to get hot to ask A/C to cool it down. Bothers me more that it took this long to think of this. Almost 61 years old and I couldn't figure out that reflecting the sun was the answer.... amazing.