Plaster Positive Model

Used for vacuum forming and heat molding of shell

Made from negative model of foot captured in plaster of paris slipper cast, foam impression or STS Sock.

Was for a long time the gold standard

Advantages:
Accurate model of foot
Can use many different materials for orthotic shell

Disadvantages:
Physical storage of cast can be space intensive, depending on how long the lab keeps the cast for remakes or repeat orders.
Can break easily if dropped or during vaccuum forming — it can’t usually be replaced unless get a new negative cast.