Elastic thread is a little bit thicker than normal thread and it stretches more. Elastic thread is used with stretchy fabrics like jersey cotton, or if you’re sewing with an elastic waistband.
Wind it by hand to prevent snapping the thread. Don’t pull the thread as you are winding it. If you pull it too tight it may unravel. If you wind it on the machine it will pull the elastic, causing it to break.
Elastic thread is only used in the bobbin, and not as a top stitch. If you use it as a top stitch, the thread will snap and possibly damage your machine.