My hot tub cover was getting very heavy, so I replaced one of the foam inserts. The foam insert was also cracked, so rather than buy a new cover, I tried inserting a new styrofoam insert. I picked up the styrofoam insulation from Home Depot (4′ x 8′ x 2″), traced the old foam insert onto it, then cut it out. I then smoothed and contoured the edges by running the shop vac over the edges. I wrapped the foam in plastic vapour barrier and Tuck taped the seems to prevent moisture from entering.
The original styrofoam was contoured. It was roughly 3 inches in the centre and tapered to about 2 inches to the edge. The foam I bought was just 2 inches throughout.
So far it seems to be doing the job. The hot tub cover is about 6 years old and moisture penetrated the old foam which made it very heavy.
Post time: Jun-19-2017