The present invention relates to a transparent immobilization device which is able to be molded direct on a patient and which is provided to cover at least a part of a patients' body that needs to be fixed, supported and/or immobilized, which immobilization device is at least partly made of a plastic material. The immobilization device is at least partly made of a sheet of a material comprising at least one thermoplastic elastomer which is a copolymer of ethylene with at least one α-olefin having 3-10 carbon atoms, or a blend of two or more of such copolymers. The present invention also relates to a method for producing such an immobilization device, according to which the plastic material is first heated to a temperature which is 15-20° C. above the melting temperature, then cooled to a temperature which may be supported by the body and molded on the body part of the patient that needs to be immobilized.