The mainsail is usually the main and most important sail on single mast sailing yachts. It is the main sail driving the yacht. It is larger than the jib or genoa, which is located in front of the mast. Since the surface of the sail is quite large, it is reinforced with special slats to give it a proper shape. In the past it was made of wood, but nowadays it is made of light plastic. These slats are usually mounted vertically or horizontally in special pockets sewn on the sail. In practice, the term "battened mainsail" is used for mainsails with horizontal slats, which are rolled up on the boom, as opposed to mastheads rolled up in a mast.