What Type of Foam is Used in Boats?

People and boat building companies have used a number of different kinds of foams in boats. What is the best foam for a particular section of the boat, or for a particular purpose?  Those questions will help us zero in on the best answer. 

-Satisfy Coast Guard Requirement

​​If the purpose of the foam is simply to satisfy a Coast Guard requirement for a certain amount of foam flotation, then one might choose any number of brands of foam that have been Coast Guard Approved.  BUT if the location for the foam is below the water-line, for a high-quality, very long-term solution, you should choose a foam that substantially exceeds the basic Coast Guard standard.  For as anyone who has worked around boats for long will tell you, very often when digging into sections of boats below the waterline that any “flotation” foam they find, is often very waterlogged.  Thereby adding very many pounds of weight to the boat, instead of light, positive flotation (the opposite of its intended purpose). 

-Location Is Above Waterline & Used for Insulation

 If the location is above the waterline and the purpose is to supply insulation to the craft, then regular home spec., closed cell (2 lb./cu.ft), spray foam insulation will be fully adequate.