Plastic welding is the fusion of thermoplastics. Thermoplastics are flexible or moldable synthetics that must reach certain cooling and heating temperatures to create products. The first step to begin the weld is pressing. Pressing requires compression to keep parts in the appropriate place and to improve the liquefied stream across the interface. This is used in both the heating and cooling phase of plastic welding. The pressure is normally applied by a machine for precision and control. Once the polymer substance is pressed it is then heated to acquire the desired shape. The shape is dependent upon molecular structure of the material, the temperature, and the mold. The heating of the material is crucial for clarity and clearness. Once the material has been heated and worked it moves to the cooling stage. In this stage the welding is completed, and the plastic becomes solid.