First of all, welcome to TDH. And second, that's a good question-one which I really would like to hear the answer to myself. I would guess that if the cardboard was reinforced so that the weight of the fiberglass material slathered in resin doesn't distort the natural shape of the helmet-that stuff seemingly could be rather heavy...That's but a guess however, as I took the easy route and bought one of Sarges 'mystery" helmets and didn't get into the resin and fiberglass etc...