Wood is amazing stuff. Cellulose fibres are about 50% carbon and are long, thin and light. And crossed hatched in plies and resin has great dimensional stability. Plywood springs back rather than bends, it absorbs sound, doesn't melt, is a good temperature insulator, is non-conductive, can be drilled, filled, sanded, painted etc. And economical so in all very hard to beat. And wood grows itself so it's renewable. Richlite is similar to plyboard, ie: paper and wood fibre held together with resin, so might make great playfields too.