A biomechanical custom made foot orthosis (10) and a method for making the same. The orthosis (10) has a thermoformed flexible top layer (12) made of a first moldable synthetic rubber material, and a thermoformed flexible reinforcement core layer (14) made of a. moldable core material that is molded onto the top layer, (12). The core layer (14) has a posterior end (16) aligned with a mid anterior plantar prominence (K) of a calcaneus bone (C), and an anterior end (18) aligned near metatarsal-phalangeal joints (J) of the foot. The orthosis (10) also has a thermoformed flexible bottom layer (20) made of a second moldable synthetic rubber material that is molded onto the top layer (12) and the core layer (14). The core layer (14) is more rigid than the top and bottom layers (12, 20). The orthosis (10) corrects anatomic biomechanical deficiencies of the foot and ensuing body deficiencies.