fc × mbs ÷ sf = wll

Minimum Breaking Strength (MBS): the maximum amount of force a material can withstand before it breaks completely under a straight pull. The cord manufacturer should specify the MBS.

Working Load Limit (WLL): the maximum weight as defined by the manufacturer that a user is allowed to apply to a lifting medium in the performer flying system.

Fiber Class (FC): A classification used in cordage standards to group rope fibers by mechanical behavior. Class 1 fibers (nylon, polyester, polypropylene) have moderate stiffness. Class 2 fibers (HMPE/Dyneema, aramid, LCP) are high-modulus fibers. Modulus (elastic modulus) is a measure of stiffness — how much a material resists stretching under load.

Composite Fiber (Hybrid Construction): A cord made with two or more fiber types in its load-bearing structure (for example, a polyester sheath over an HMPE core). In cordage standards, if any load-bearing component contains Class 2 (high-modulus) fiber, the cord is classified and derated as Class 2, since the lowest knot efficiency governs overall strength.

Derating Cord: The MBS of the cord needs to be derated by 50% for Class 1 fibers and 70% for Class 2 fibers to account for knots and terminations, which reduce the strength of the cord.

Characteristic Load: the maximum force applied to the system resulting from normal intended operating conditions while the system is at rest or in motion.

Safety Factor (SF): the ratio between the designated working load limit (WLL) and the load the equipment is expected to fail at. When selecting an appropriate cord for use with body suspension, a safety factor of 10 needs to be employed. This safety factor takes into account dynamic forces and unknown variables but not terminations.