If you wish to make Permanent Press pants with perfect Permanent Press effect, you should order the TC fabric from a dyeing /finishing mill “Post cured”. In that case the mill will supply youth fabric treated with chemical (resin) but with last process “baking: not done, leaving it for you to do after cutting.
After the fabric is cut before sewing operations, you should press the cut pieces to leave a crease where you want the crease to stay permanently. Generally you would do that on the center crease of the pants. When pressing is done, you get all the cut pieces through the oven to let the heat finish off the last process to produce the permanent press effect. When the pants are finally finished, the center crease so made should stay on the pant permanently. Please note pot cured fabric must be finished off by oven baking otherwise; permanent press effect will not be achieved.
Post cured fabric are usually those for making dress pant type of pants, not for jackets or shirts where you do not need neat creases to stay fresh. In fact, now a days most TC you order are pre cured because most garment factories today are not equipped with the baking oven to handle post cured fabrics. However when you order TC permanent press fabrics, you really should make sure with the mill that you are getting what you plan to have.