Abstract: An impression of a portion of a human body is made by forming a preform of tandard profile of polymeric material with shape memory that is substantially rigid at ambient temperature and flexible and elastic at a higher working temperature, bringing the preform to that working temperature, and placing the preform on that body portion. After cooling of the preform to below the working temperature, the preform is removed from the body portion and a positive model is cast from the preform. The preform is then returned to the working temperature without physical constraint, whereupon the preform resumes its standard profile and so can be re-used a number of times. The polymeric composition comprises at least one elastomer and one polycaprolactone diluted in a composition of solvents that dissolve the polymers. The elastomer is polyurethane. The composition of solvents comprises dimethyl-formamide to dissolve the polyurethane, toluene to dissolve the polycaprolactone, and methylethylketone as a buffer.