Insulating the hull questions.

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Have some 1/2" sheet pieces of very light white foam loose in the back of the truck. I knelt on it, put tool boxes on it, stuffed it around things that needed to be imobilized. Tough material. Been there for a year or more - I mean it has some permanent dents - but I won't bet on it. It's amazing stuff. You see it used for packing.
It's called Ethafoam. It was real cheap when I bought it at TAP Plastics. It is bendy and pliable, cuts with knife or scissors. It's CLOSED CELL polyethylene foam. It would be perfect insulation if you could find something to stick to the hull with!
One of its great qualities is that nothing sticks to it!

Another material worth looking into is Tekfoil (and other brands) which is various layers of bubblewrap and foil and sometimes polyethylene. The foil is coated when it's an outer layer. There are seam tapes and double sided tapes to stick it. I'd experiment with carpet tape.
Again no mastics I'm aware of. But I've heard some people are putting it into boats. To keep condensation at bay imco you have to have to glue whatever insulation tight to the hull without holidays. Dunknow?

Years ago I got a deal on some 1/2" Ensolite - it's a tough, light tan colored, closed cell pvc rubber.
Hours of research to find a non-lethal mastic led me to a waterborne gel/paste called APAC 564. It's a 'green' flooring adhesive for all kinds of vinyl flooring products. Have glued some 'panels' onto the hull in one cockpit locker.
The job was a PITA because I did it after I closed it in - like an idiot. But they're stuck and seem ONE with the hull.

There must be some mastic that will glue polyethylene - maybe APAC has it.
You may think that this is the Age of Aquarius BUT it really is the Age Of Glue.
Thing is if you got hot summers or you're going tropics, the fiberglass is going to get really hot. The stickum has to hold through what?... a 150 degree range?

I also found some nice beige 1/4" cut-pile polyethylene auto 'head-liner' material. Not really insulation. Actually the doors & footwell in my truck is covered with similar stuff. (Polypropylene pile is commonly used for auto and boat liners - imco we want material that doesn't hold water. Water FALLS out of my polar-fleece jackets, made from recycled p.ethylene 7-Up bottles. The auto liner is the same stuff.
(Head-liner in the Dodge is a thin fabric not glued very well to friable foam.)
'Carpet liner' has an amalgamated backing allows it to be cemented onto boat surfaces. Intend to glue it onto the Ensolite in storage areas. In other lockers, imagine cutting hull carpets to fit, but hanging them in with velcro hook & loop, so they can be removed and washed. They'll have insulating and cushioning value in difficult access areas.

Consensus has it, we should insulate the hull above the waterline where rapid changes in temp and humidity causes condensation. So I'll be attempting this. Another good reason is that, as with any insulation, we're warmer in the winter and cooler in the summer. Thinking Hawaii!


May have got the cement thing covered with the acrylic pudding APAC564.
But what do I know about the outgassing of super-heated pvc foam. Pvc does NOT have a good rep. MSDS sheets exist to reveal info that's hidden by 'trade secret' clauses. They've got carcinogentic plastisizers and other ingredients that makes PVC NON-recyclable. Plastic bad boy that has contaminated the oceans and toxified landfills everywhere on the planet.
All clear plastic films are also implicated in toxic horror stories.
So lining the interior of the boat with this stuff is something to be real about.