I use a Bosch electric heatgun, variable up to 500°Centrigrade. Hold the heat about 6 inches away, and do a small section at a time. A kitchen oven will work as well, on medium heat, but experiment a lot first.Place the plastic on it's mold, and put the mold on a flat piece of steel or aluminium. Leave the oven door half open, and grab the whole lot out of the oven just before it reaches the final shape required.Use oven mitts, please!
Do NOT think of cooling it off with water!!!
WAIT for it to cool!
Works for Lexan, Perspex etc.
Stu