A thermoforming aid for use in creating a thermoformed impression of an object such as a dental arch. The thermoforming aid has a thermoformable sheet which has inherent tendency to curl when unsupported, and a curl-resistant element which prevents the thermoformable sheet from curling. The thermoforming aid makes a person's task of placing a sheet of thermoformable material, especially a very thin sheet having an inherent tendency to curl, in proper position in a thermoforming machine less difficult and time-consuming.
