A formable cast (100), brace (180) or splint is provided herein which comprises a padding (101), an outer shell (103) spaced apart from the padding, and a ridge (109) disposed along the perimeter of the shell. The ridge, shell and padding define an interior space (115), with a curable polymeric material disposed in the interior space. The curable polymeric material undergoes a phase transition, upon curing, from a liquid or gel phase to a substantially rigid solid phase. The cast (100), brace (180) or splint may be readily customized to the patient by fitting the cast to the patient's body, positioning the cast in the desired orientation, and curing the curable polymeric material through exposure to actinic radiation or by other suitable means.