I have a wooden garage with a metal roof. I want to make it as cool as possible on the inside. I will have the windows and door open most of the time. I don't really want to use fiberglass bats. I've been considering spray in foam insulation. Which would be the better choice, open or closed cell? I've heard one of these types attracts a lot of dirt. Are there other drawbacks, or options available? I just want to insulate under the metal roof, and I don't intend to insulate the walls. I live in deep, east Texas forest, where it is hot and humid in the summer and not that cold in the winter.