After reading that Energy Secretary Chu said we could all save money with white roofs, our family thought we would try it. We got some white roofing compound, which reflects, 95% of the light, and spread it with a broom. Combined with white exterior walls, new insulation, and exterior shades on the sunny sides of the house, we sometimes gain 22 degrees of difference between exterior and interior temperatures in the middle of the day. Things inside can heat up in the evening after several days of a heat wave, but we just open up the house and run a fan. By morning we're ready for the next day. We have no air conditioning and don't miss it!