This heavyweight elastic is a flat knitted elastic, also referred to as Corset or Medical elastic.  It is often seen in support belts, and offers a firm hold.  It is a non-roll elastic.  It is customary and usual for splicing to occur within the spool.

Wholesale Flat Knitted Corset Elastic 217 - Black 4".  Priced per 50 yard roll.

70% Polyester, 30% Rubber

80% stretch, firm, great recovery.

Non-roll: width remains 4" when stretched.

Medical grade for use in back braces (hence the corset moniker).