Water Tight Foam?

Check up on the difference between 'porosity' and 'permeability'. Next describe the intended application etc and describe within allowable limits. I don't intend to sound like a pedant goosemydog, but for a serious answer you need more than that. At present I can only tell you that my padded cell is padded and watertight. No 'dis' intended, but more info from you would help - I cant provide, but others may with more from your good self.

I'm thinking in terms of a foam that won't absorb condensation, as in a hot tub cover. They all seem to use cheap styrofoam that lasts 2 or 3 years, then gets water-logged.

'hot-tub' isn't a commonly known term in the UK. If it's cheap-' use-it-and-bin-it' ? I can't picture exactly what you mean. Any chance of a picture - I'd love to try offer novel suggestions and I think others would too. The more info you give, the more you can get back. Hot tubs have been on CR4 threads before - a bit more info might lead you there. Hope you can get back with more ( remember the audience isn't all American, Brit etc) info.

Both DOW Chemical and Owens Corning have a closed cell insulation that they claim will not take on moisture. This is not entirely true and they will eventually take on moisture but it will take much longer than what is currently installed (white bead board). You could install it and then try to encapsulate it in an EPDM rubber membrane (pond liner rubber). This will help keep the moisture from attacking the insulation. The combination should make the insulation last about 25 to 30 years.

Cheers

I was sort of thinking rubber type membrane, but didn't like to say ! Foam is good - you just have to seal the outside.

You are right, if you can put a barrier of some kind between the water and the insulation you can keep the R-Value at a good rate. Once the insulation becomes wet it looses this R-Value. The barrier has to be a synthetic, plastic (poly or PVC) or rubber.

Another term used for this tub is a 'spa', although I think of a spa as a building you relax in. It's a fiberglass tub holding anywhere from 300 to about 800 gallons of warm water you sit in, party in or work out you aches and pains in. The cover is to keep the BTU's in to save on expense of heating the water. It must be able to withstand constant heat, ozone and chlorine bombardment. Does this help?

Thanks goosemydog, now I see. Some while back a question was asked about help in designing a School project - a portable hot tub. I never did find out why anyone would want a portable one. It sounded like they wanted one to tow behind the car when going on vacation in Alaska !

For a good source, google mcmaster-carr.

I bought some rubber there I used for flood panels. They had a page that explained all the different types as well as durometer (hardness) and it included all types rubber and foams. Very informative. Their prices arent bad either.

I'm ashamed that I am not 100% certain of the name. I know that "syntactic" does not fit the normal definitions, but, I'm pretty certain that this is what the non-crushable-by-depth foam is called that gets placed (about 2 inches thick) all around our diving bells, to aid in keeping the (saturation) divers from freezing to death, when they are not OUTSIDE the bell, with hot water circulating into and out of their suits.

This stuff lasts an eternity, even at 1000 FSW (1000 x .45 = 450PSI)... thus, all of our routine ultrasonic surveys are performed from the interior, where we need only shoot thru the epoxy paint.

Search for "submersible", "diving bell" etc manufacturers. If you can't find anything, I can get the info after I return to the office following next week's Conference in L.V.

Best wishes ~

All gas filled foams crush at depth. There is one way to do this:-

Add glass microballoons to the mix. These are tiny glass spheres that you can buy pretested to proof depth to add to the polymer. They are not compressible and they add some void volume to the foam and reduce the thermal conductivity.

drill here

http://www.google.ca/search?hl=en&safe=off&q=glass+%2Bmicroballoon+%2Bdeep&btnG=Search&meta=

You have had some great answers, but how about placing a large sheet of polythene on the foam when new and using a flexible polythene/styrofoam compatible spray glue, join one to the other...? That way you have the cheap Styrofoam, but moisture is kept away. Check the glue first on a small area before using as many glues dissolve Styrofoam.....

If you do not mind the possible color differences, there are heavier plastic sheets used to make walls impervious to moisture, they are at least 10x more expensive than normal polythene sheeting and a lot heavier and thicker, but NOTHING gets through them!!!

I tend to favor the cheap version as it will probably last 20 years or more as it gets a chance to dry out when you use the tub....it is also more flexible and with a hairdryer, it can be made to follow curves very well when sticking!!

If one sheet is not enough, use two!!

All advice offered for free, but I have not actually tried this at home, sorry. Hopefully it will give you a few ideas of your own!!

What about the buoyancy aids used to help people learn how to swim? They are probably polystyrene.

Neoprene?