Fancy aluminum foil.

My next step was to insulate the roof to help control the heat. It doesn't get that hot where I live, but it wouldn't hurt to try to control the temperature a bit. I settled on this stuff. It's called radiant barrier. It supposed to keep the area it's insulating about 10 degrees or so cooler. When I was reading up about it online, it was being used in houses in areas with much more extreme temperatures, like Arizona. I originally tried to use the kraft-faced insulation (you know, the pink fluffy stuff that looks like cotton candy?), but it was too cumbersome to use. This solution was much easier to install and has been suitable for my needs.