That is the standard ribbed metal available at Lowe's and Home Depot. It has held up quite well. Those beds are four foot by twelve foot. I used heavier wood that I had laying around the shop to connect at the corners and and also to bridge the span in the middle to prevent the sides from blowing out. They seem to have held together fairly well. They are about two years old now. The round beds were the first we made. They were considerably more aggravating to assemble because the panels had to be bent against the reinforcing ribs, but they are quite rigid and only required wood supports at the seem. The round beds are more than four years old. We are also testing an all wooden bed treated in the Sho Sugi Ban wood preservation method. I will do a write up on that in the near future.