During a recent trip to IKEA (how we hate that we hate-love that store) for a couch, we ended up taking home a huge sheet of this amazing thick honeycomb cardboard - as a bonus result, we got two chairs for the price of one!
The seat panels are doubled up for extra strength, but that only gave us enough material for a single sheet on the side panels. We'd would like to double these as well, so that we can get rid of the some of the cross members (the ones that stick out).
The cardboard is 30mm thick, and has a honeycomb pattern for the support material.
Cutting the seat panels.
This cardboard is pretty fun to work with. It cuts really fast with a jigsaw, and puts out almost no dust. Note to NDC, go to IKEA and pick up more free honeycomb cardboard for more explorations.