Which type of expanding foam?

[84EdH]

I have done some stringer and deck repair and want to apply some insulating/flotation foam. I tried some with a 4lb rating but it did not expand nearly as much as I anticipated.

Which foam is recommened for filling voids between hull and decking. I hope to gain flotation, sound reduction, and hopefully firm the deck just a bit. Any suggestions on where to buy it?

thanks

Ed