Ya know, I never researched the differences. I asked the gals @ sewing center and trusted what they gave me but I had a heck of a time with it. The Nylon is performing way better for me and it is probably that stretchy you were talking about that made things crazy.Nylon sounds good! I never was good at sewing stretchy fabrics so the thought of stretchy thread in a sewing machine makes my eye twitch...lol.
WI CBL gal said she uses filament because it is clear. I don't think this thread needs to stretch, I mean, Im not a seamtress but I don't see why it would.