Insulation is one of the greater energy-saving expedients. Adding or replacing old insulation, fixing drafts and shading or insulating non-cored laminate are just some of the easy things you can do to reduce your energy bill and make life on board more comfortable. However, for many boat owners deciding on which insulation material to use is the hardest part of the job.
There are a number of insulating materials to choose from, each with their own advantages and disadvantages. The key to choosing the right boat insulation is to consider the permeability of the material and how it will interact with water. Porous materials like Rock Wool require vapour sealing to prevent moisture passing through the material and condensing on the hull, where it may cause unseen corrosion. Foam insulation boards and Thinsulate can also suffer from condensation, unless tightly bonded to the metal and vapour sealed, but they are less costly than Rock Wool.
There are also blown in foam insulations, but they have a serious fire risk and must be carefully applied by a contractor. In my opinion the best choice is spray foam, which can be applied as a DIY kit or by a contractor and is impermeable to moisture. This is the ideal marine insulation solution as it is extremely thermally efficient, soundproofing and moisture tolerant. Icynene spray foam insulation can be used in steel hulls and wood framed boats, and is safe to install in any climate.