A custom foot orthotic and a system and a method for designing of a custom foot orthotic. The method includes: receiving 3D scan data of the patient's foot； receiving plantar pressure scan data of the patient's foot； establishing a desirable pressure distribution； generating an underfoot elevation profile relative to an elevation profile of the patient's foot in the 3D scan data； determining an internal density profile of the resulting foot orthotic 3D model by superimposing the desirable pressure distribution over the resulting foot orthotic 3D model and reducing or increasing density in regions of the foot orthotic 3D model based on the difference between an expected pattern of support and the desirable pressure distribution； and outputting the 3D model of the custom foot orthotic.
