Because of the sheer size and scope of the plastics industry, the title developments in plastics technology now covers an incredibly wide range of subjects or topics. no single volume can survey the whole field in any depth and what follows is, therefore, a series of chapters on selected topics. the topics were selected by us, the editors, because of their immediate relevance to the plastics industry. when one considers the advancements of the plastics processing machinery (in terms of its speed of operation and conciseness of control), it was felt that several chapters should be included which related to the types of control systems used and the correct usage of hydraulics. the importance of using cellular, rubber-modified and engineering-type plastics has had a major impact on the plastics industry and therefore a chapter on each of these subjects has been included. the two remaining chapters are on the characterisation and behaviour of polymer structures, both subjects again being of current academic or industrial interest. each of the contributions was written by a specialist in that field and to them all, we, the editors, extend our heartfelt thanks, as writing a contribution for a book such as this, while doing a full-time job, is no easy task.