Kevlar is the trade name of a para-aramid fibre developed by DuPont in the 1960s and, from the 1970s onward, the material that first gave sailmakers a fibre that would not stretch. Golden-yellow, five times as strong as steel by weight and with a modulus far higher than polyester, it became the load-bearing yarn in racing laminates and the original tape in UK Sailmakers’ Tape-Drive® construction. The beginner needs to know that Kevlar is a very strong, very low-stretch fibre used in performance sails. The experienced sailor adds two cautions: Kevlar degrades in sunlight faster than polyester, and it does not like being folded or flogged, so the same property that makes a Kevlar sail hold its shape makes it demand careful handling.
What Kevlar Is and Why It Matters
Kevlar is a synthetic polymer whose molecular chains line up along the length of the fibre and bond to one another in tightly packed sheets. That structure gives it exceptional tensile strength and stiffness: a Kevlar yarn stretches only a fraction as much as a polyester yarn under the same load. For a sail, stretch is the enemy. A woven polyester genoa that grows fuller and moves its draft aft as the breeze builds is a sail whose shape is being decided by the wind rather than the designer. A sail whose load-bearing fibres barely stretch keeps its designed shape from the bottom of its wind range to the top, points higher and heels less.
Kevlar is not used as a woven cloth on its own. Its fibres are too slippery and too vulnerable to abrasion for that. Instead it is laid as straight yarns, either woven into an open scrim or laid unwoven in oriented layers, and laminated between films of Mylar polyester with adhesive under heat and pressure. The film carries the small off-axis loads and stops the wind blowing through; the Kevlar carries the big loads along the direction the yarns run. Light taffetas of woven polyester are often added to one or both faces for chafe and UV protection, at a cost in weight.
Kevlar in UK Sailmakers’ History
UK Sailmakers’ Tape-Drive® construction was built around Kevlar. Rather than relying on a laminated cloth whose yarns run in fixed directions, Tape-Drive laid narrow tapes of unidirectional high-modulus fibre – Kevlar at the start – along the computed load lines of the sail, radiating from the corners and following the paths the loads actually take, over a lightweight base laminate that mainly kept the sail airtight and held its shape between tapes. The result was a sail that put strength exactly where it was needed and weight nowhere else. Later generations of the idea moved to carbon and aramid blends and eventually to the Titanium™ and X-Drive® sails of today, but the principle of fibre along the load path, first proven with Kevlar tapes, is the direct ancestor.
Cruising and Racing Perspectives
For the racer, Kevlar and its aramid relatives are the point of entry into shape-stable sails. A Kevlar laminate jib holds a fine entry and a straight leech through a wide range and does not go baggy in a puff, which translates directly into pointing and speed. Racers accept the trade: a Kevlar sail has a shorter life than a polyester one and needs careful storage, sun protection and a crew that does not let it flog.
For the cruiser, a pure Kevlar racing laminate is usually the wrong choice, because cruising sails live in the sun and are asked to last a decade. Cruising laminates with taffeta both sides and blends of polyester and aramid or Spectra offer much of the shape-holding benefit with far better durability. Where a cruising sailor does have Kevlar sails, a sun cover on the furled genoa, a well-fitted boom cover and rolling rather than flaking are the habits that keep them alive.
Frequently Asked Questions about Kevlar
Why are Kevlar sails gold or brown?
The fibre itself is a natural golden yellow. As it is exposed to UV it darkens toward brown, so the colour of an older Kevlar sail is a fair indicator of how much sun it has seen.
How long does a Kevlar sail last?
It depends on use and care far more than on age. A club-racing laminate with taffeta protection and a good cover may give five or more seasons of good shape; an unprotected sail left flogging and folded can lose its edge in one.
Kevlar taught the sailmaking world that a sail could hold its shape rather than merely survive the wind, and everything from Tape-Drive to today’s load-path sails grew from that lesson. Treat it with the respect its stiffness demands, keep it out of the sun when it is not working, and it repays you in height and speed.