High-Modulus Polyethylene synthetic mooring line — strength similar to steel wire at a fraction of the weight.
Regulatory detail & full definition
Common brand names Dyneema, Spectra. Significantly safer than wire in snap-back (low elasticity = low stored energy when it fails), and lighter for crew handling. Susceptible to UV degradation and creep under sustained load; OCIMF MEG4 mandates inspection cycles and load-monitoring. More expensive than polyester.