Only 2C I can offer is that I ALWAYS heat seal the edges of all the nylon I've sewn. Haven't had any unravel yet....I also no only fold the edge over once....I'll fold it a second time to be certain that the cut edge is deep inside the 'hem' or 'edge'. It provides for a stiffer edge though.....but if you are making a holster for a knife or gun....well maybe that's a good thing.
Hope this helps.
CJ