Anti-torsion cables are an essential piece of kit for top down and straight luff furling systems. As the name implies, top down furling needs to start from the head of the sail. So, the rotation of the drum at deck level needs to be efficiently transferred to the head. Anti-torsion cables are specifically designed to resist twisting. The better the cable, the less turns required at deck level to rotate the upper fitting.
Straight luff furlers furl from the tack and head simultaneously so also require cables with excellent ant-twist (torsion) properties. Additionally, these sails rely on the cable for luf tension in the sail. This means that cables for this type of sail need to be both strong and low stretch. The Harken Reflex cable is not suitable for this application unless supported by an additional dyneema line. However, it has the highest torque resistance making it the best line for top down furling.