James L. Throne 
Technology of Thermoforming [PDF ebook] 

This thorough text covers thermoforming processes and products. It moves from a relatively simple approach to more technical in-depth consideration, featuring examples and guidelines to illustrate all technical aspects.
Contents:
– Definitions, History, Methods, and Equipment
– Polymeric Materials
– Heating the Sheet
– Stretching the Sheet
– Cooling and Trimming the Part
– Molds
– Parts Design
– Producing Sheet and Film
– Latest Technologies
– Set-Up Protocols, Trouble-shooting, and the Economics of Thermoforming