It was a custom-designed (but cheap) system. We bought a bunch of warped seconds of a material called "Skate Ramp" from Paperstone, which is manufactured out here in Washington. It's basically a 1/4" exterior grade product to be used for, you guessed it, skate board ramps. They used to advertise their seconds online. It only cost $1/square foot. Then we mounted to on 1x2 vertical battens, attaching it at the edges so we didn't have to drill through the material.

Awesome. I've used Paperstone for countertops, but that is cool that you used remnants in this way. Did you just do a rainscreen-type application? Was the attachment something similar to what you'd use for Swiss pearl or Hardi panel?

Yes, it's a rain screen. Then it's just screws into the 1x2 battens with big washers holding the paperstone in place. In places we needed to put a screw where there wasn't a batten we just used a little 1x block.