My 55' alloy sailboat has 4" or about 100 mm of mineral wool insulation everywhere above the waterline. It is spun volcanic ash so does not absorb
water, is fireproof to about 2000f and is organic. Or so they say. I like it as I can weld on top of it without setting the
boat on fire.
It is made by Roxul from
Sweden, I believe. The downside is that it is heavy and bulky. I put about 1000# or 450 kg of it aboard. A
trade off I suppose, as it takes a candle to heat the
boat now, and it is cool in summer.
There are many other products, I just did not want to add a lot of nasty chemical products into my living space.
Greg