The most common template that I use is the Belt Template. This is made from a 1/4 inch piece of plywood, cut to 2 inches high and about 4 inches long, to simulate a belt.

You then heat the kydex, and wrap it around the template to allow it to cool. The nice thing is that you can further use a sander to shape the template to whatever curves you may like to have in the finished product. Here is an further image of the shaping process using wood to form the rigid bends.