A dried and cured roll of Poplar bark, that would be suitable for container and basket making.  Poplar bark(Liriodendron tulipifera) has been used throughout history for the making of containers, due to its quality of being able to be stripped from downed trees, and scored and folded into many shapes.  It measures 21 inches long, and when rolled out and laid flat it has a width of 16 inches wide across.  The thickness is 3/16th of an inch, which is ideal for folded baskets.  To make pliable again for layout of projects, it simply needs to be soaked in water overnight.  It can then be scored and folded, or dried around a form to make a solid tube.