Heat set pleated fabric is one of my favorite things in high fashion. They can also be found in consumer fashion (chiffon pleated skirts are so IN right now!) and there is also tons of it at thrift stores!
Heat set pleats are made by basically pressing fabric at high heat into pleats. It’s pleated at such high heat that the pleats will stay unless heated to that temperature or above again. But it’s so high not even your dryer can reach it. The pleats will stay pleated through washing, hot weather and humidity. Heat set pleats can be found all over the place with lightweight fabric.