A few years ago my son was wild for a slap watch. A slap watch has a watch band that stays stiff and flat until you slap it against your wrist. The force of the slap makes the band curl up. Seems like a good idea for the battens of a furling sail. The battens are stiff when the sail is unfurled. But roll up the sail and the battens curl up. Primrose Fry Technologies Ltd (PFT), a British firm, has devised a batten product called Flattens that does just that. Flattens provide stability to the leech of the sail when it is rolled out and then the force of rolling in the sail causes the Flattens to roll up as well. PFT claims that when furled, the sail not only stays put, but can actually hold a tighter furl than a sail with no battens at all. PFT wrote in a press release: "The secret has been to construct Flattens from a highly advanced performance material in combination with critical geometry that means the Flattens are stable rolled up around the headstay or unrolled in the sail. Just like when a retractable tape measure coils away, the Flatten has been engineered to roll up smoothly, neatly and reliably as it approaches the headstay. As Flattens have such an outstandingly high bend and compression stiffness, the sail designer has the scope to incorporate more roach than is possible with traditional furling battens, so allowing the option for more area to be built in to the sail."
RFT says its Flattens product is for racers and for cruisers. See a video below of a racing jib equipped with Flattens being rolled and unrolled.