The Biscuit Maker is made of Urethane coated nylon, chosen for it's strength, ease of custom shaping/conformation, and comfort. It also allows for variable design depending on where the users pain is located. The straps that hold the robot to the skin ensure that the material expands inwards, applying force in a more targeted manner.
In each image, you'll see drawn circles. These highlight where there are pockets of air, filled and emptied by a programmable pump.