I recently acquired a hot tub for free (the right price). The frame was rotted and in working on replacing the boards one at a time I found a large amount of wet insulation. The insulation was soft and foamy like a seat cushion when dry but I believe open cell and once wet would not release it's water. I removed all this wet insulation and rebuilt the frame. I am now working to reinsulate before winter and have a few questions that hopefully someone here can provide some guidance on. I tried Great Stuff and found I have about 14 cubic feet of insulation to replace. A can only fills about 1/4 of a cubic foot. At local prices that put my insulation at over $300. I tried the triple expanding and it seemed to fill more but I wasn't able to get a handle on how much. I began looking for alternatives. I found a pourable Urethane insulation that should fill the spaces for about $130. It claims to have an r-value of about 6 and expands 20-30 times depending on temperature. However the test samples I did last night while expanding wonderful and definately closed cell and resistant to water are very rigid when cured. Has anyone else had experience with this type of product. I am concerned about the rigidness of the new insulation when adjacent to the existing foamy insulation. It doesn't seem to disturb the existing insulation when expanding but definately does not have the flexibility the existing insulation had once cured. I had considered using rigid sheets to fill the spaces but that seemed like a lot of cutting and fitting, and the skirts don't allow for sheets around the perimeter. Any thoughts or experience would be greatly appreciated. Tim

Got myself and old 80's Jacuzzi Avanza and looking it over I find it lacking in insulation compared to new models.
Been doing some internet research and found this site:

http://www.foampower.com

Which sells Handi-Foam , When you click on Learn More it says under ideal applications: Repair and Replace insulation for Hot Tubs, Spas. (UL-94 Rated) the price seems good for 4.5 lbs: $42.95 , Has anyone tried it?

4.5 lbs produces 22 board feet. A board foot is 1 foot by 1 foot by 1 inch. This size kit wont cover a single sheet of plywood even 1 inch thick.... something to think about

OK, so its worse then the equivlent of Great Stuff?
http://greatstuff.dow.com/greatstuff/cons/choosing.htm

I thought I would update this link on the hot tub I was rebuilding. I did wind up using the expanding foam that was designed for marine floatation use. It took far more then I ever expected but worked great at filling a number of voids the original manufacturer had left open. After one winter of using the tub things seems to be working fine. (I had some thermostat issues but that is another story). The electricity cost to heat and maintain has been about $50 a month which didn't seem bad to me for a 6 person tub. Only time will tell if the foam breaks down, but so far it has been great.

Do you have a Manufacture or website for the foam you used?

I am still looking for something to insulate the tub and help keep the heat in.

Am considering this procedure at the moment,

Aluminum insulation applied to the exposed sides of the tub and wrapped around the pipes to retain that heat.

Then use fiberglass insulation, dougle bagged in sealed platic bags to fill up the voids and then sealing those bags into the voids with some sort of foam insulation, extruded around them for a tight void filling seal.