The sheathing is a fiberous material pressed like chipboard. It is engineered to dampen the sound of the AC system in your home. Lighter than the same thickness of plywood, but heavier than foam. In my application, it is sandwitched between a 1 1/2" x 1 1/2" aangle frame and the aluminum top. For my installation, weight has not been an issue. The egg crate material will be much lighter, but I chose to use the sheathing for three reasons: 1. It is what the canopy manufacturers in this area of Texas use. 2. It is less expensive. 3. I put a layer of paint on it, so iit won't soak up water and mold if I wash it off. For your application, egg crate might be better. Try 3M "Super Weatherstrip Adheasive" as a glue. Also called "Gorilla Snot". Body shops use it. Good glue.
Photo above. How big is your canopy ? I have a piece of Aluminum left over. Another advantage of aluminum I left out: The material I bought has a diamond plate mirror finish on the top, like the tool boxes at Tractor supply but thicker, so probably reflects 95+% of the radiant heat. Important in Texas.
JRPoux