My concern with cardboard is that there is going to be some lower breaking point (especially the fork portion of the bike) due to the stress of riding it on uneven surfaces, debris getting caught in the spokes, or because of user motion. Carbon fiber forks have failed before causing catastrophic injury and death. Depending on tests, it may be an accident waiting to happen.
http://www.chairigami.com
My concern with cardboard is that there is going to be some lower breaking point (especially the fork portion of the bike) due to the stress of riding it on uneven surfaces, debris getting caught in the spokes, or because of user motion. Carbon fiber forks have failed before causing catastrophic injury and death. Depending on tests, it may be an accident waiting to happen.