According to the Free Dictionary, cardboard is made from either pasted sheets of paper or the pulp derived from pressed paper pieces. Therefore, cardboard can contain a wide variety of different paper types and thicknesses.
Because cardboard is constructed from innumerable paper sources, it cannot be defined as one specific entity. In other words, not all cardboard pieces are not made from the same materials, but all cardboard pieces do have a uniform appearance. These similarities arise from the process of making cardboard, which meshes individual pieces of paper together to form a rugged, stationary structure that can hold objects of all sizes for indefinite time periods.