A foam luff provides better sail shape over a wide range of wind conditions. It automatically flattens the sail as it is furled creating less heal, more drive and a happier crew when conditions get rough.

There are extra layers of cloth at the leach and foot due to the hems and the cover on a furling sail. Therefore, as the sail is furled, it becomes more full, just what you don't need in heavy air.

The foam adds additional thickness to the furled sail in the middle of the sail's hoist. The first rotation of the furler adds this thickness to the roll and effectively flattens the sail as it is furled.

Note how the width of the foam layer tapers from the center of the luff toward the head and foot for a smooth transition.

Note the standard tell tails too!