This new type of closure was from the early 1990s as an alternative to natural cork because of the there increasingly occurring Korkschmeckers popular. The plugs are usually made of a rubber or Teflon mixture. Currently three methods are used. In the injection molding process, the plugs are cast individually, they are usually hard and very smooth and not very flexible. In the extrusion process (extruder = push out, drive) a viscous, foamed plastic mass is pressed through a nozzle in a continuous process. From this resulting strand then the plugs are cut off. In coextrusion (combining materials), a core of homogeneous, foamed plastic material is introduced into a tube made of plastic, which ensures radial elasticity. This type is considered the most suitable in terms of flexibility, tightness and uniformity.