I've never used this particular foam board before - it has a paper covering on it which adds quite a bit of rigidity at the expensive of, well, being paper.
Since I had two sheets of foam, I stripped the one of its paper covering. This was a messy process, even though there are videos on YouTube showing people doing it in minutes, it took me ages with a hose pipe to get the thing clean. That's when I discovered just how much rigidity the paper actually added.
Anyhow, the build is coming along nicely, although I do need some more foam glue and carbon fibre spars. I think that if I had kept the paper layer on, the carbon fibre spars wouldn't even be needed. The whole thing will be "laminated" with duct tape anyway, which makes it substantially tougher and somewhat water resistant.
For scale, the long ruler in the picture is 1 m.