12 mm 'SuperSpeed' is quality double braid with a HMPE (high molecular weight polyethylene(often know by the trade names Spectra and Dyneema)) core with a polyester cover made by Southern Ropes. Break load 13200 lb. This line have a vastly superior breaking strength and considerable less streth that double braid polyester liunes.  Ideal for blue water cruiser and club racers halyards, etc.