Net radiation is an essential forcing of climate in the lower layers of Earth's atmosphere. In this paper, radiation balance is measured in clay soil and green grass, and is compared with three urban materials. These materials: asphalt, concrete and white painted elastomeric polystyrene roofing sheet are widely used in Mexicali, Baja California, México. This study was carried out during August of 2011, the hottest time of the year. The 24-hour average values of net radiation found were: 137.2 W·m −2 for asphalt, 119.1 for concrete, 104.6 for clay soil, 152 for green grass and 29.2 for the polystyrene insulation. The latter two types of materials are likely to be the most effective in reducing urban heat island effects. This variation in the radiation balance has widespread implications for human living conditions, as land cover change tends to be towards surfaces that have higher levels of net radiation.