Attic Foil Radiant Barrier - Garage Doors
Some various instructions on using various materials for garage doors, etc. they even recommend other products that they don't sell, such as the foil faced poly-iso, because you can get it locally and it fits nice. Also addresses ventilation ideas if keeping heat out is the major concern.
These are some solid ideas I need to pursue some day, since my door faces west and my garage heats up fast in the afternoon. Well worth reading about on this site.