Sailcloth is cloth used to make sails. It can be made of a variety of materials, including natural fibers such as flax, hemp, or cotton in various forms of sail canvas, and synthetic fibers such as nylon, polyester, aramids, and carbon fibers in various woven, spun, and molded textiles.

Viking longships used wool for sailcloth. The cloth was woven in one of three ways, according to locality and tradition: plain weave with individual threads going over and under each other, three-shaft twill with two threads going over and under at each cross thread, and four-shaft twill with thread interwoven with two threads at a time in either direction. Such was the practice from the 11th through the 14th centuries.

Doek is Dutch for cloth, which evolved into the English word "duck" in reference to sail canvas. Duck was typically made from cotton or linen (flax), with some use of hemp. These natural fibers have poor resistance to rot, UV light and water absorption. Linen is stronger, but cotton is lighter. Linen was the traditional fiber of sails until it was supplanted by cotton during the 19th century. At first cotton was used as a matter of necessity in the United States as it was indigenous and the supply of flax was periodically interrupted by wars such as the War of 1812, during which demand for sailcloth for military use was high. As sail size grew linen was too heavy to be practical so cotton became more popular. Cotton did not substantially replace linen worldwide until the end of the age of sail; however, in some cases the strength of linen was preferred for some types of sails. It was not until the late 20th century that natural fibers were replaced by synthetics in mainstream use. Cotton sailcloth is still used for sportswear, upholstery and draperies. The traditional width for carded cotton sailcloth in the US was 23 inches (58 cm) while the British standard was 24 inches (61 cm).

In the ancient seafaring traditions of the Austronesian peoples of the Indo-Pacific, the sails were traditionally made from woven panels of pandan (screw pine) leaves and lashed with ropes usually made from coconut coir. These sails were integral in the subsequent migrations (c. 3000 to 1500 BCE) of the Austronesians from Taiwan, to Island Southeast Asia, Micronesia, Island Melanesia, Polynesia, and Madagascar. Some examples of pandan mat sails were so finely woven that they were compared to "coarse linen" by the Spanish and "dressed sheepskin" by the Dutch.

Specific examples of sails made from pandan mats in Austronesian-speaking regions include the sails of the fayang rafts of the Amis people in Taiwan, the various bangka of the Philippines, the kabang of the Moken people, the wa of the Caroline Islands and Yap, the tepukei of the Taumako Islands, the oblong sails of the canoes of the Ninigo Islands, the baurua of the Gilbert Islands, the drua of Fiji, and the waʻa kaulua of Hawaiʻi, among others. The technology of pandan mat sails were also introduced to non-Austronesian peoples via contact, like to the Yolngu of Australia.

Sails could also be made from woven mats of other similar plant leaves and fibers, including those from sugar palms, buri palms, and nipa palms.

The characteristics of a sail are due to design, construction and the attributes of the fibers, which are woven together to make the sail cloth. The following sections discuss the attributes of fibers assuming a good design and careful construction. According to Mahr, there are six key factors in evaluating a fiber for suitability in weaving a sail-cloth:

There is no perfect solution since in most cases the increase of one attribute generally results in the decreased attractiveness of another. Reduced stretch generally also reduces the flexibility causing a trade-off of performance for durability. Solving both problems generally sends the price out of range for most sailors.