Stay away from expanding foam for models. It rarely ends well. There are plenty of more stable options. But if you have built the boat properly then it won't sink anyway.

Colin

If you have a sealed buoyancy chamber it surely needs nothing else it it?? Putting anything in a sealed chamber only makes it heavier.

If you think water might get into your sealed chamber then perhaps it is not really a sealed chamber??

Ordinary expanded polystyrene is the way to go if you have doubts on the efficacy of your sealed chambers. Only sufficient is needed to stop the boat from sinking.

Ashley

Apart from its knack of absorbing water, either from contact with liquid or just getting it from damp air (and boats operate in damp conditions), most users use far too much, not really allowing for it expending as much as it can.

Expanded polystyrene packing or similar, hacked to shape works well. Or similar packing noodles. Or, if you can forego the joy of popping them, bubble wrap sheets.

I imagine that the last thing wanted in a buoyancy chamber is soggy ballast that cannot be extracted and/or dried.

The only time I have used expanding foam was when I had a water issue in the carpet carrier (as the deck just fitted over the hull and water was coming in the bow).

SO I squirted foam in the front compartment….BUT this didn’t matter as the top was of course open, so I left it a few days and then trimmed it flush. Water still gets under the fore deck but runs off a bit further on off t( foam.

Absolutely would use it for anything enclosed.

Ashley

Pool noodles are simply tubes of "Closed Cell Foam" as I mentioned above.