Waistband Stabilizer 1.25" widea 2 yards + How-To-Use from Londa
Call it Armoflexxx, as I became aware of it back in the 80's from Palmer/Pletsch - or Ban-Rol, but this monofilament stabilizer is just the BEST waistband 'filler'!  It is strong but supple - bouncing right back up after it bends with you.  
My How to Use Instructions include complete directions off how to use; even how to utilize some elastic with it for a waistband application that stretches.