There was a issue with the company making the resin that is used in the production of hypalon, but I hear that a firm in Japan is now back at it. I believe that a firm by the name of Burke is producing hypalon.
The vents are just a piece of PVC, maybe 8" long, installed horizontally (flat) at the top of the liner, around the perimeter. Ours was installed by Environmental Liners out of CO, but I just learned they are no longer in business.
Ours is a plain liner, no covering, but it is a specific purpose pond.
