a method of producing a container of polyethylene terephthalate or similar thermoplastic material from a tubular blank of amorphous material . a mechanical forming element moves a transitional zone between amorphous material and thinner oriented material stretched to flow during simultaneous elongation of the blank in the direction of movement of the transitional zone . the stretched and oriented material is heated to a temperature higher than the temperature of the material immediately before stretching . as a result , the internal stresses produced in the material during earlier stretching are relieved . heating causes the length of the material in the direction of stretching also to be reduced . each subsequent forming stage for shaping the container takes place at a temperature lower than the temperature at the immediately preceding forming stage .