This is how bottles are made. Vacuuum forming Softened material is drawn into a mold.
Compression modling A heated mold is squeezed around a pre-formed blank.
It is slower, but the material does not flow as far. Injection molding A power or pellet is liquified, injected into a mold, cooled under pressure, and ejected. This forces the mold shoes apart slightly, which stretches the two tie bars that hold the shoes. This stretching creates a tension, much like a spring, in the tie bars which presses back against the mold , holding it together during injection. When the carriage cylinder sees a pressure of 1950 PSI, a pressure switch is tripped, starting injection.