I'm considering using foil-backed bubble wrap on the underside of my attic rafters and possibly in the crawl space under my house. The crawl space foil is because we plant to install radiant floor heating at a later time. I've looked at local retailers and priced the product. I'm acting as the GC of the house so I should be able to get it as a contractor. My question:

Does anyone know of a mail order/manufacturer I can order the stuff from? Is there a better place to get it other than the typical home improvement store?