How to use Gutermann Maraflex Stretch Thread
Gutermann Maraflex 120 is made from high elastic polyester filament that has built in intrinsic elasticity that is ideal for highly elastic seams.
Gutermann Maraflex 1500M thread spools
It is suitable for stretch knit clothing, shoes and leather goods, for elastic decorative seams, etc. Offers a smooth, pucker-free appearance. For maximum stretch, Maraflex should be used in both needle and bobbin or looper threads.
Maraflex is amazing as a topstitching thread when sewing with stretch knit fabric.  This is a little video showing just how much stretch it gives these straight stitches used to topstitch the neck band on a tshirt.  Wow!
Gutermann Maraflex is currently available in 17 colours and on spools measuring 1500M.
GutermannMaraflexStretch thread