Rodger,
This is a dilemma that I'm fighting with now. It is more important in a
steel boat, but the problem is the same. I think you will find that the
sprayed urethane foam is superior because of it's ability to seal off the
damp air from the cold metal surface much better. If you were to us sheet
foam, you will also have to provide an airtight vapor barrier as well to
prevent condensation. In both cases, please realize that the foam surface
must be painted for fire retardation and liquid absorbtion reasons.
Steve

"Roger Mcmillan" wrote in message
...
Hi,

I'm about to start building a 37ft Van de Stadt from an aluminum kit. One
area of boatbuilding that seems to get skimmed over in all books is
insulation.

I have access to sheets of polystyrene. Is this any good for metal boats?
Or should I stick with polyurethane?

I'm also investigating a Swedish product called Moniflex which is used
extensively in passenger trains because it's light, fire-resistant and
flexible, which sounds perfect for boats. Does anyone know anything about
it?

Many thanks
Rogermac