Insulation. Two coffee cups of different construction showing differences in insulation. The cup on the left is made of expanded polystyrene, a very good insulator, so may be held comfortably despite the coffee being hot. The cup at right is made of a waxed paper. This is less insulating, and would be uncomfortable to hold, so a sleeve of corrugated cardboard is added to allow the user to hold the cup. A plastic lid is added to further help keep the beverage warm. While the polystyrene cup is simpler, it is not recyclable and so has been largely replaced by the paper version in high street coffee shops.