Originally Posted by
whitewood
Cub,
I sell a lot of Paulownia to hollow surfboard builders and have talked to most of them about their boards. I have never heard of any of them putting foam inside the board. Some attach the strips for the skin to a sheet of glass/epoxy to make a single section and the 'glue this to the frame. The outside is then glass/epoxy and this provides the strength and waterproofing needed. The big thing is to have a drain plug to control air expansion and contraction within the board. Some guys even have the drain plug as a release valve to maintain an even pressure within the board.
Having said that I can see no reason for not putting foam inside the board if that is what you want to do. It will add some weight but the final decision is yours.
Whitewood