Corrugated plastic. I took my time, copying the curvature of the hood (which mimiced the bumper as well). Then, I made 4x "wedges" for the sides and 2 braces (which gave it the final angle, 2 braces were placed in ~1/3rds under it). Finally, a thin strip on the back for further bracing... then taped it all together and taped it on! Meant to snap a pic before it went on... whoops
I can take further pics of the back side of, though, if you want more of an idea of it. I plan to extend it to cover the blinkers and either relocate them, or use some thin plexiglass to have them blink through it.
I threw together a little mspaint diagram of what the cuts looked like...
Driving around today, top I saw was 197*F on a mix of city and highway, but often going lower than that.