Flax, Linum usitatissimum, is an upright annual plant growing to 1.2 m (3 ft 11 in) tall, with slender stems. The leaves are glaucousgreen, slender lanceolate, 20–40 mm long and 3 mm broad.

The flowers are pure pale blue, 15–25 mm diameter, with five petals; they can also be bright red. The fruit is a round, dry capsule5–9 mm diameter, containing several glossy brown seeds shaped like an apple pip, 4–7 mm long. It is a member of the genus Linum in the family Linaceae. It is a food and fibre crop that is grown in cooler regions of the world.Linum usitatissimum is native to the region extending from the eastern Mediterranean, through Western Asia and the Middle East, to India. It grows best at northern temperate latitudes, where moderately moist summers yield fine, strong but silky flax. In Poland, a hectare of flax plants yields1.5 to 3.5 tonnes of fibre. Like cotton, flax fibre is a cellulose polymer, but its structure is more crystalline, making it stronger, crisper and stiffer to handle, and more easily wrinkled.

Flax fibers are mainly used to make linen. More than 70% of linen goes to clothing manufacture, where it is valued for its exceptional coolness in hot weather – the legendary linen suit is a symbol of breezy summer elegance. It is also used in making high quality household textiles – bed linen, furnishing fabrics, and interior decoration accessories. Shorter flax fibres produce heavier yarns suitable for kitchen towels, sails, tents and canvas. Lower fibre grades are used as reinforcement and filler in thermoplastic composites and thermoset resins used in automotive interior substrates, furniture and other consumer products.