Experiments with acoustic microscopy at an ultrasonic frequency of 50 MHz were unsuccessful; however, experiments that used swelling techniques with various solvents, relief polishing, and heat treatment were successful. The experiments revealed that thermomechanically treated regions of a polymer have a higher swelling capacity under the influence of solvents than untreated regions. Results show that polymers have a "mechanical memory." The heating process showed similar "memory effects" to those observed by Hosemann et al during experiments on the deformation of polyethylene. Apparently, each crystallite is transformed by stretching into microcrystallites that lie together like a string of pearls and form parts of the so-called ultrafibrils of the stretched material. The domains may only regain their original shape near the melting point if the microcrystallites are interconnected by chain molecules that do not lose this contact during the stretching process. The tie molecules are able to raise the entropy of the colloidal structure to the highest possible value, and the sample returns to its original shape. 4 figures and 14 references