Making Sheets of plastic or Calendering      

Calendering is a method of taking plastic pellets and rolling them hot to make them into sheets. Almost like rolling pastry. The resulting sheets can be as thick as 25mm or as thin as cling film. Sometimes, as with the wheelbarrow liners, the sheets are cut into thin strips and woven to make them into a strong woven cloth.

The animation below is not brilliant but it shows how plastic particles are fed into a hopper and heated to then be rolled between rollers until the plastic is the required thickness. at the end of the process sometimes a sheet of material is introduced into the rollers to give the appearance of a material product. A lot of hold alls are like this with a material on the out side and a smooth plastic on the inside.

Don't forget, woven nylon sheets and Vinyl sheets are are flexible enough to fold away. (Like with a deck chair phone thingy). Look further down for a better animation (inside the box would be heaters).