a sheet of polymer material is secured between a pair of clamping members . the sheet is directed through a localized heated region to provide a localized heated portion of said sheet . a first one of said clamping members is pulled away from the second clamping members to stretch said sheet and create from the localized heated portion of said sheet a neck - down region . the neck - down region separates providing a pair of neck - down region portions and a reduced thickness portion or stretched portion of the sheet between said neck - down region portions . one of said neck - down regions propagates along unstretched portions of the sheet as the movable clamping member moves away from the fixed clamping member while the other neck - down region remains adjacent the fixed member . this propagating neck - down region portion of the sheet is kept within the localized heated region by moving the localized heated region at a rate related to the rate which unstretched material of the sheet is fed into the neck - down region portion . while the neck - down region portion is maintained within the localized heated region , an electric field is applied to the neck - down region portion to polarize the film .