 Metal has a low thermal mass, meaning it doesn't store and retain heat from the sun. Next, metal roofing today has heat reflective coatings applied to it, and that helps prevent heat buildup, and it also reduces air conditioning requirements during hot weather. And finally, if you go with a metal shingle roof, well, that has airspace sort of built into it right under the metal, so you have a thermal break between the metal and the roof decking, and that can also enhance the energy efficiency.