A Polyamide, it is used in spinnakers because of its light weight, high tensile strength, superior abrasion resistance and flexibility. However, it has a low modulus allowing too much stretch to be suitable for upwind sails.
Nylon is more susceptible to UV and chemical degradation than polyesters and its physical properties can change due to moisture absorption.
A polyester based fibre, a aromatic polyester – half polyester, half aramid. As in aramid the aromatic ring makes it strong and stable, but has the benefits of a long chain molecule. Classified as a liquid crystal, as its molecules can form crystalline structures whilst still liquid. Gold in colour, has a modulus similar to aramid, but has less strength loss with flex. This is a benefit in endurance applications and for cruising sails where durability is key. Additional advantages of Vectran fibre include zero creep, high chemical and abrasion resistance and high tensile strength. The UV endurance is inferior to PET and PEN, but the degradation levels off over time, while aramid continues to degrade.
Polyethylene terephthalate (PET) is the most common fibre used in sailcloth. PET has excellent resiliency, high abrasion resistance, high UV resistance, high flex strength and low cost. Low absorbency allows the fibre to dry quickly. PET has been replaced by stronger fibres for most serious racing applications, but remains the most popular sail cloth due to lower price and high durability. Often referred to as “Dacron” (the brand name of Dupont’s Type 52 high modulus fibre made specifically for sailcloth). Allied Signal has produced a PET fibre called 1W70 polyester that has a 27% higher tenacity than Dacron. There is a wide range of tenacities (strength) and Shrink Rates available. Woven PET for sailcloth uses High tenacity/High Shrink yarns.
PEN (Polyethylene naphthalene) commonly known by Honeywell’s trade name “Pentex”, is another kind of polyester fibre, which stretches only 40% as much as standard PET fibres, but about twice as much as Kevlar 29. Because it only shrinks about a third as much as a good PET, PEN can not be woven as tightly; thus, woven PEN must be impregnated with resin making sails prone to damage from improper use and handling. PEN is better suited for making laminated sailcloth.
UHMWPE (Spectra and Dyneema)
This fibre gets its huge strength from its extremely long chain, rather than a series of highly stable rods. This explains the great flex fatigue property. The creep factor, the long chains slowly easing past each other with constant load over time has been a problem, but the modern versions have largely dealt with this. The fibre is not affected by flex, UV or abrasion. Offers superior UV resistance (on par with PET), very high initial modulus numbers (similar to Carbon Fibre), superior breaking strength, and high flex strength. It does not shrink much under heat, and therefore is not suitable for structural woven fabrics. Its use in laminates can be problematical due to its lowish melting temperature.
A high modulus synthetic fibre made from carbon atoms. Unaffected by UV exposure and provides exceptionally low stretch. Each carbon filament thread is a bundle of many thousand carbon filaments. A single filament is a thin tube with a diameter of 5–8 micrometers and consists almost exclusively of carbon – arranged in a regular hexagonal pattern. Used also to reinforce composite materials – Carbon fibre reinforced polymers.
The predominant fibre for racing sails since it was introduced. It is stronger, has a modulus that is five times greater than PET, and about twice as high as PEN. An aromatic polyamide fibre is similar molecularly with Nylon. Its ability to resist stretch, and withstand loads and abuse before breaking is the measure of everything else used today in sails. Aramid fibres have a poor UV resistance (loses strength twice as quickly in sunlight as PET) and a loss of strength with flexing, folding and flogging. Known often by its brand name of Kevlar (Dupont), or Technora (Teijin), has a modulus and strength similar to aramid but a higher resistance to flex fatigue. The fibre’s lower UV resistance is often enhanced by dying to black the naturally gold fibre.