I use copious amounts of vet- bed and paper but have a friend who uses only shredded cardboard. It certainly looks very snuggly and clean, hers are reared outdoors so it wouldn't be suitable for inside. From memory the board is about quarter inch square and she has it quite deep. I tried it on my outside kennel for the adult spaniels, it was very warm and toasty but made a hell of a mess in the run even though we have baffle boards on the enterances, lots of sweeping.
I think your safest bet would be to stick to vetbed and paper, shavings can get into eyes, ears etc and some bits are very sharp. Not worth the risk.