Equipping roofs with highly reflective material (such as aluminum) increases a roof's albedo and will help reduce the amount of heat it absorbs, hence, the amount of energy needed to cool the building it is on. Green roofs or “living roofs” are a popular choice for thermally insulating a building. They are also popular for their ability to catch storm-water runoff and, when in the broader picture of a community, reduce the heat island effect (see urban heat island) thereby reducing energy costs of the entire area. It is arguable that they are able to replace the physical “footprint” that the building creates, helping reduce the adverse environmental impacts of the building's presence.