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.
If it is a matter of keeping cool and not heat in. I would suggest ventilation in an area above a ceiling. Install a ceiling that has a cavity that you can blow air into and out of on each end. This will circulate the hot air out and cooler air in being heat rising and cool air naturally sinks.