You will often hear sailmakers talk about a "fill oriented" or a "warp oriented cloth. Sailcloth is woven on a loom. The loom beams long yarns down the vertical direction of the cloth. These vertical yarns are called warp yarns. The loom also shoots fibers horizontally across the loom, allowing the warp yarn to go "over and under" it. the yarns then "interlock" together, however one yarn is always straight, and the other yarn "crimps" around it.
Warp & Fill
Warp yarns run vertical along the roll of the cloth. Fill yarns run horizontal. A fill oriented cloth has a straight fill yarn and a crimped warp yarn. A crosscut sail is fill oriented, meaning that the fill direction is stronger than the warp direction, due to the crimp. Crimped fibers can be pulled until they are straight. Over time and under pressure, this will happen, causing the fabric to stretch in that direction.
The bias direction of cloth is the diagonal direction, where there is no yarn directly aligned with the load. This is the weakest direction of cloth, and is what we spend much of our time developing. Challenge Fiber 104 "interlocks" more than any other type of cloth. The interlocks create mechanical advantage, which strengthens the bias. We engineer our constructions to math the load of a sail.
Learn about how your sailmaker cuts a sail to optimize the threadline strength in a crosscut and tri-radial sail (click here).