Abstract: The present invention provides a new and improved positioning device for stabilizing a subject on an operation table without a clinician's manual fitting. The inventive positioning device comprises a mattress/pad with a shell filled with a substance and a vacuum outlet on the sidewall of the shell. The invention also provides a warming device for preventing hypothermia of a subject on an operation table. The inventive warming device comprises a single cavity or an array of closed cuboid cavities contained in a shell and filled with a phase change material (PCM) in a form of liquid, and a triggering means for activating nucleation of the phase change material, which leads to an exothermic crystallization of the material to start the heat emission. The invention further provides a combination device that performs positioning and warming functions simultaneously.