POLL: best sidewall material

Very noobie here, still at the scribbles stage, but also collecting a file of resources - UK suppliers of the bits n pieces I'll need.
Loving the level of detail on the excellent benroy plans, which leads me to think "what do you favor?" A solid 3/4" ply sidewall (like the BENROY plans) or the method I was thinking of: a sandwiched side made up of 1/4"ply either side of a 1" thick frame, with urethane board to fill the voids. I figure that would be lighter, and still good & strong.
Thanks y'all
Loving the level of detail on the excellent benroy plans, which leads me to think "what do you favor?" A solid 3/4" ply sidewall (like the BENROY plans) or the method I was thinking of: a sandwiched side made up of 1/4"ply either side of a 1" thick frame, with urethane board to fill the voids. I figure that would be lighter, and still good & strong.
Thanks y'all
