Bast fibre (also called phloem fibre or skin fibre) is plant fibre collected from the phloem (the "inner bark", sometimes called "skin") or bast surrounding the stem of certain . Some of the economically important bast fibres are obtained from herbs cultivated in agriculture, for instance flax, hemp, or ramie, but bast fibres from wild plants, such as Urtica dioica, and trees such as Tilia, willow, oak, wisteria, and mulberry have also been used. Bast fibres are soft and flexible, as opposed to from plants, which are hard and stiff.
Since the valuable fibres are located in the phloem, they must often be separated from the woody core, the xylem, and sometimes also from the epidermis. The process for this is retting, and can be performed by micro-organisms either on land (nowadays the most important) or in water, or by chemicals (for instance high pH and chelating agents), or by . In the phloem, bast fibres occur in bundles that are glued together by pectin and calcium . More intense retting separates the fibre bundles into elementary fibres, which can be several centimetres long. Often bast fibres have higher tensile strength than other kinds, and are used in high-quality (sometimes in blends with cotton or synthetic fibres), , yarn, paper, composite materials and burlap. An important property of bast fibres is that they contain a special structure, the fibre node, that represents a weak point, and gives flexibility. Seed hairs, such as cotton, do not have nodes.
Bast fiber from oak trees forms the oldest preserved woven fabrics in the world. It was unearthed at the archeological site at Çatalhöyük in Turkey and dates to 8000-9000 years ago. Bast fibres are processed for use in carpet, yarn, rope, geotextile (netting or matting), traditional carpets, burlap, paper, sacks, etc. Bast fibres are also used in the non-woven, moulding, and composite technology industries for the manufacturing of non-woven mats and carpets, composite boards as furniture materials, automobile door panels and headliners, etc. From prehistoric times through at least the early 20th century, were woven from bast strips in the forest areas of Eastern Europe.
Where no other source of tanbark was available, bast has also been used for tanning leather.
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