Real flax linen is a yarn or fabric made from the fibre of the cultivated flax plant, named Linum usitatissimum.
This domesticated species is believed to have been developed during cultivation. It is a cellulosic plant fibre, or bast fibre. It forms the fibrous bundles in the inner bark of the stems of the plant. The flax plant is an annual that grows to a height of about a metre. The fibres run the entire length of the stem and help hold it upright. The fibre strands are normally released from the cellular and woody stem tissue by a process known as retting (controlled rotting). In Ireland this was traditionally done in water in rivers, ponds or retting dams.
Today the term linen can be confusing. Linen was once in such common use that it became a generic word for articles or garments, such as sheets, tablecloths, or underwear, formerly made of linen. Today these items are usually made of other fibres, especially cotton or polyester/cotton. These are not real flax linen.