Loose-luff furling sails have grown in popularity with the rise in quality of torque ropes. Torque ropes refer to the category of rope that does not rotate (or not much) under tension. When you pull it tight, and turn one end, the other end turns. In a headsail application, this lets you use it in the front of a jib without a permanent furling unit with aluminum extrusions up the forestay, the kind almost all furling systems use. Instead, a Code Zero furler is used, either the continuous line variety, or a more traditional single-line style. The furling drum shackles to a spliced loop (reinforced) in the rope at the tack of the sail, and its counterpart head swivel shackles into the loop at the head. The only thing connecting the furling parts is the torque rope, enclosed inside the luff of the sail. While less-expensive low-stretch rope options can be used on a continuous line furler that wuill still roll up the sail if you're going to take it down immediately, if you're going to leave it up and furled, torque rope is the only way to make sure you get a tight roll, especially at the head, which can sometimes stick out unfurled and tempt the breeze to pry it open and unfurled.
Scott Loomis from our Stuart loft just installed a torque rope jib on an Aerorig that had no forestay. Rather than add metal weight, the owner chose a torque rope setup to hang the jib between the end of the forward boom and the top of the mast. The following photos show the result.
Here, the sail is at full deployment, sheeting nicely to the single-point sheet location.
Here is the sail furling:
And here is the head of the fully-furled sail:
Torque ropes have evolved nicely, and allow loose-luffed headsails without permanent stays. They need certain rigging changes, like (ideally) a two-to-one low-stretch halyard to prevent luff sag, and a strong attachment point on deck. With these, torque rope sails can serve as inner heavy-weather jibs behind a genoa on the forestay, or as Code Zeros or light genoas forward of the forestay. Both could be left up and furled when not in use, or easily removed for added safety.