The cast is designed to be a rectangular pouch that is 20x30x2.5 cm. The enclosure is made of heat-sealable plastic, and a nozzle is attached and ensured to be airtight. Within the enclosure are 20 stacked layers of sketchbook paper, and a 100g pouch of 83% coffee grains, 15% carbon flakes, and 2% aluminum wire mesh by volume. Velcro is glued along the outside of the enclosure, so that the cast remains secure around the limb while allowing for adjustments depending the limb diameter of the person .
The cast must stiffen sufficiently under a vacuum
The cast must hold a sufficient vacuum during its use
The exterior package and its sealant must be airtight and durable; seals must not break down as the cast is bent and warped with use
Ideally, the materials should also remain intact when exposed to the environments the users will subject it to, whether it be extreme moisture, cold, etc.
The cast must maintain stiffness even after multiple use cycles
Surface roughness and other factors contributing to friction should be maintained even as the layers are compacted and possibly sheared against each other
The packaging for the grains should not leak to either the exterior of the cast or above the neutral axis of the cast, where the stiffening effect of grains is lost
The cast must be comfortable to the user
The grains must be very fine or easily deformable
The vacuum must not cut off user’s circulation
The cast must be superior to equivalent, existing products in terms of:
Stiffness
Penetration resistance
Time taken to activate to full strength
Conformability