A kit and method are presented for making a mending device, such as a splint, for immobilizing a body part, such as a limb. The kit includes a formable material and heating source. The heating source is used to selectively heat the formable material to an elevated material, molding the formable material into a required shape for the mending device and allowing the molded material to cool to room temperature and become hard again. The formable material may be molded on or around and in contact with the desired body part. The heating source may include a chemical composition that is selectively activated, for example by adding water to it.