Cardboard is mostly used for protection, or to build something for a project of some sort, or it is used for packaging a package. Kids could use cardboard as an castle or a fort, sleeping in it. There was one time, in 3rd grade, my teacher told my class to do a project using cardboard. My Dad literally did all the work (Thanks Dad) and he made a marble racer thing. I''m pretty sure it was trashed by now, but I will never know. Cardboard has many uses including using it for a project, protecting yourself against something(I wouldn''t use cardboard), or protecting a box inside a box.