Sunlight turns to heat when it travels through the windows and is bent in the process. My theory is, keep the heat from going through the windows.

If your car is going to be parked for long periods of time, make a cover which you can plop over the top, covering all the windows. Two lengths of 60 inch material, purchased at a fabric store and stitched together lengthwise, ought to do it.

Next you need to weight the corners to keep the wind from blowing it off. I believe that four sponge-rubber balls (such as children used to play with) would provide the weight and would never damage the car if they banged against it.

My husband and I disagree as to whether the cloth should be white (for reflection) or black (for shade). What do you think?

I have been using a cloth cover on the OUTSIDE of my windshield for years, and I'm convinced it works better than those reflective screens on the inside. I put the windshield wipers over the edge of it to keep it down.