say, is that a weave?

Big Pimpin’
Sail cloth has gone through multiple iterations over the years. Woven polyester long ago gave way to high-tech laminates and composites that offer tremendous weight to strength performance. While the fibers that provide this strength vary in modulus, flex, UV and tensile strength, most laminates are still dependent on standard polyester films that encapsulate the fibers and provide off-angle stability. Polyester films have been the primary base since the late 1970s but gradually sailmakers have recognized that these films aren’t as long lived as the fibers they protect and support.
Over time polyester films may succumb to UV degradation and abrasion which can break the windows between the fibers, while long term off-angle loading can cause the films to shrink. One means to minimize ageing is by adding a layer of fabric to the outer film, providing a UV-stable surface that offers more off-angle stability and enhances abrasion resistance.
This type of fabric has been in use in cruise laminates for years and provides incredibly long-lived sails. The one drawback, of course, is the increased weight incurred with the added taffeta.
Learn more here.