Spinnakers and gennakers are built from nylon because they must be light enough to fill, resilient enough to survive repeated collapse and refill, and compact enough to live in a bag. This page is about downwind nylon only. Code Zero belongs with Upwind & Code Zero Sailcloth because its load-bearing structure is laminate.
This page applies to spinnakers and gennakers.
Why nylon for spinnakers and gennakers
It is very light for its strength. A spinnaker has to fill in wind you can barely feel, and a heavy cloth simply hangs. Weight per square metre is the first requirement and nylon wins it.
It stretches, and that is useful here. A flying sail collapses and refills constantly, and refilling is a shock load — far higher than the sail’s steady load. Nylon absorbs that shock by stretching. A cloth that did not would transmit the whole impulse to the corners and the seams.
This is the property that makes nylon wrong everywhere else. On an upwind sail stretch means the shape changing and the boat pointing worse. On a downwind sail the shape is much less critical and the shock absorption is worth more.
It packs small. A large sail has to live in a bag on a boat.
It recovers. Nylon returns to shape after being loaded, which matters on a sail that is loaded and unloaded thousands of times.
What it does not do
It goes soft when wet. Nylon absorbs water and loses stiffness. A spinnaker that has been rained on is measurably fuller than the same sail dry, which is why sails are dried before being stowed.
It is UV-sensitive. More so than polyester. A flying sail left in the sun degrades faster than its handling suggests, and this is one reason downwind sails live in bags rather than on the boat.
It is not stable enough for a tight angle. That is why a Code Zero uses a different, load-bearing laminate structure rather than nylon; the Code Zero material logic is covered separately.
Nylon weights and working range
Nylon is described by weight, and the weight is what defines a flying sail’s role more than anything else.
The lightest cloths hold their shape in almost no wind, which is exactly what a light-air running sail must do. Their ceiling is low: in fresh conditions the cloth stretches, the sail goes out of shape, becomes unstable, and is at risk.
Mid-weight cloths are the general-purpose answer. They will not fill in the very lightest air and they are stable across the range where most boats spend most of their time. If you are buying one downwind sail, this is where it sits.
Heavier cloths are stable in fresh wind and cannot be made to fill in very little. They are for sails whose job is control rather than power.
Two things follow from this. Cloth weight and sail geometry are one decision, not two — a very full light-air shape in heavy cloth is good at nothing, and a flat heavy-wind shape in light cloth will not survive the conditions it was built for. And a downwind sail’s usable wind range is set largely by its cloth, which is why the numbered roles on a gennaker map so directly onto weights.
The nylon we offer
Our downwind range is Challenge nylon in three working classes:
| Cloth | Typical role |
|---|---|
| Super Series 33 | Very light-air racing sails where minimum weight matters most |
| Fibermax 44 | The all-purpose choice for mixed VMG and reaching programs |
| Fibermax 64 | Larger sails and stronger wind ranges where extra structural margin matters |
These are not three price steps for the same sail. The cloth weight changes the wind range, the shape the sail can carry and the load it can survive. Available colours depend on the selected cloth and its coating.
What this means when you choose
For a spinnaker or a gennaker, you are choosing a nylon weight, and the weight comes with a wind range and a shape. Tell us the wind and the angles you want and the weight follows.
Coating, porosity and colour
Nylon is not defined by yarn weight alone. The finish changes how tightly the sail holds air, how it behaves when wet and how much water it carries. A firmer coating generally improves stability and water repellency, while a lighter or uncoated finish reduces weight and cost but can allow more porosity and faster loss of shape when wet. We only offer the coating and colour combinations available for the selected cloth in the configurator; the sailmaker confirms the valid combination against the intended use.
Ageing and care
Nylon ages from ultraviolet, from flogging, and from being stowed wet. Of the three, flogging does the most damage in the least time — a sail left to flap while a crew sorts out a problem is being destroyed at a rate nothing else matches. Dry it before it goes away, and do not let it flog.
Nylon also needs to be protected from ultraviolet and repeated chafe. A bag, dry storage and sensible recovery routine are part of the material’s service life.
More on the materials themselves
For Code Zero and other low-stretch structures, see Upwind & Code Zero Sailcloth.
Configuring this at SurgeSails
For a spinnaker or gennaker, Cloth offers the nylon weights, with Base Color and Panel Colors selecting the scheme — on these sails the colour is the cloth itself.
Which weight suits your sail follows from what you want it to do. Describe the wind and the angles in Design Note rather than choosing a weight directly.