Blow moulding produces hollow three Services-dimensional articles from many of the thermoplastics materials which are available as granules or powders. The simplest tool consists of two female parts which contain a cavity when closed.
Granules or powder are softened in a plasticising cylinder and extruded into a vertical tube or "parison". The soft , warm parison is surrounded by the open mould which is then closed, thereby sealing the lower end of the parison. This is then inflated pneumatically (from the other end) to conform with the surface of the mould.