Good old nylon is still considered the "right stuff" for nearly all spinnakers. It’s slightly stronger than polyester (Dacron), a bit less expensive, and its greater elasticity is, in some respects, an asset because it helps absorb shock loads and makes for chutes that are easier to fly in bouncy conditions. Of course, greater elasticity also has a downside—sail-shape distortion in stronger winds.
Nearly all lightweight spinnaker materials are, by nature, "warp-oriented" because the warp yarns (yarns running the length of the fabric) are pre-tensioned during the weaving process. The result is disproportionate crimp (zig-zagging) in the fill yarns (which run at right angles to the warp), resulting in fabrics that stretch more easily in the fill direction. Tri-radial construction takes advantage of warp-oriented styles because it ensures that the major sail loads are aligned with the most stretch-resistant axis (the warp) of the fabric.
Many spinnaker cloths are also "unbalanced weaves" with higher DPI in one axis than the other. DPI (denier per inch) is a figure representing the amount of fiber per linear inch in a fabric. When two figures are given (i.e. 30 x 40), it’s conventional to give the DPI of the warp first, followed by the fill. For example, the traditional .50-ounce construction is a 30 x 20, with a 30 DPI warp to handle the primary loads and a weaker 20 DPI fill to minimize weight. By contrast, a material suitable for all-purpose and cross-cut spinnakers might be a 30 x 40 construction, with beefier yarns in the fill direction to compensate for their greater crimp. Nearly all spinnaker fabrics have oversized ripstop yarns at intervals in both the warp and the fill to help prevent small tears from spreading catastrophically.
Originally Posted by angrysparrow
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