Well, A-class grey cardboard is the best choice. Because the leftover of grey cardboard is cost-effective and eco-friendly. Moreover, the technology is easy, not much work. It is called "enviromental " packaging.
The main characters of choosing A-class grey cardboard as following:
*the leftover of grey cardboards are packed directly from printery when they pack boxes. It is cleaner than usual waste paper.
*the toughness of grey cardboard. The maximum ability for loading stuff at a certain time.
*friability.Generally, under the outer force, paper will get teard down, folded easily. But this one is different, cause it is through some chemecial process to strenghen its' bearing capacity.