Thermoforming is a technique whereby a flat sheet of plastic is changed into a three-dimensional object with the use of heat. However, there are a lot of problems that can occur during this process and this book will provide thermoformers and part designers with an insight into the problems that can occur during the production of a product explain why problems happen and how to prevent them. Problems can be classified as uneven shapes, blisters or bubbles, poor detail, incomplete forming, sagging (excessive sheet sag, uneven sag), webbing, stretch marks, poor wall distribution, tearing the plastic sheet when forming, part sticking to the mould, part warpage, surface marking, uneven edges, raised corners, and cracking in corners. Also discussed are the different types of surface defects, their identification in plastic parts and the ways to solve the problem. All these problems and their remedies are covered in detail in this book. This book will be of use to those producing thermoformed items whether they are experienced thermoformers or new to the technique, and to designers, designing items which will be produced by thermoforming.