I recently aquired a '95 Cal Spas spa from a co-worker. The spa has been in storage for a few years. A few months ago, the co-worker had the spa installed at a new home and experienced serious leakage. He didn't want to attempt the repair so asked if I would like the spa. I accepted the offer and recently moved the spa to my house. The weight of the spa was unbelievable. The spa has full foam insulation and it was fully saturated with water.

I am now in the process of removing all of the foam (fun, fun) to locate the leak(s). I expect that the unit was not properly winterized and freeze damage has ocurred.

My question is a foam substitute for insulation. I am considering using a plastic covered fibergrass near the jets and Polystyrene on the outside walls and bottom. I know I can re-foam but repair is very difficult with the foam.

Any suggestions for insulation, other than foam?

Certainly....
I call it no foam.

I agree, no foam, just insulate the bottom and sides of the cabinet, and make sure it's wind tight as well.