They’re important because solar radiation can cause buildings to overheat if their exterior materials have a high solar absorptance. If your roof can’t reflect the sun’s heat, it’s going to be much warmer inside the home, causing you to use your air conditioner more often. Urban areas with high solar absorption surfaces will make that area’s average temperature higher than the surrounding less populated areas. This temperature change is known as the urban heat island effect. Cool roofs are a cost-effective and simple solution to urban city heating problems.