Originally Posted by MyronL
We just had a big cloudburst overhead and I couldn't find the umbrella but I had to run out to the trailer to double-check. So yes, it bends fairly easy if the ribbed seams are horizontal and you use contact cement to get it (slowly) on the first shot.
So you bent it in the difficult direction! I would have guessed the other way.
Following Myron's lead, I went out and grabbed a piece for a test. It is much easier to bend around a vertical tube (such the Myron's front box corners) with the corrugations running vertically, and it could readily bend it without kinking around a large radius (I used a round fender of a utility trailer) in either orientation. With a smaller test radius of about 20 cm (8") around a small tire, it was difficult to avoid kinking with the corrugations vertical, and took more effort but bent more smoothly with the corrugations horizontal. This was about 4 mm (5/32") thick material, sold for signage.
This stuff is typically polypropylene, which is a thermoplastic, so it would form around curves more easily and more smoothly if warmed.