integrated multi - layer roofing that includes energy - conserving reflective layers and insulation can be pre - fabricated in sheets , panels , or even complete pre - sized roofs . recycled polymers can be used for some or all of the layers , and other recycled materials such as fiberglass can be used in the insulating layer . some versions of this integrated roofing can be installed directly over roofing beams , greatly reducing the time and expense of installation . the polymer construction makes this roof lightweight and long - lasting . the reflective properties allow for increased energy capture by solar panels and reduce the ground - level effects of greenhouse gases in the atmosphere .