Materials used by the world’s leading superyacht builders are not particularly specialised, or expensive, just used in vast amounts. The superyacht yards often deploy large quantities of Rockwool, for example, available from any DIY store or builder’s merchants. They cram it into overhead voids in large overlapping slabs.
They also use products we’re familiar with such as 3M’s Thinsulate, or the US-made Reflectix or EU-made Armaflex. Metal yachts, and even some composite ones, also use spray foam, much as you might find in your attic.
Tanks are aften sprayed with a thermal barrier coat of foam to stop big heat differences between the tank’s contents and the interior of the yacht. Big temperature differences lead to condensation
rockwool is used in huge quantities to fill every underdeck void. This is especially useful in countering loss or gain of heat in areas with temperature extremes, such as the tropics or polar regions
An aluminium bulkhead has been sandwiched, first with rockwool (brown), and then with Thinsulate (white) and finally with a foil barrier. This will preserve localised temperature zones and dampen resonated noise