The hull of the boat is made from a dense closed-cell foam called Plastazote. It is tough totally impermeable and can be heat formed and welded with a hot air gun. It's 4m long and the beam can be up to 700mm. It is very light.
The hull is stiffened with wooden gunnel strips.
For more information and instruction sheets, visit the website below.
This is an Opensource project, and all of the information is freely shared.