Bast fibre is a type of plant fibre that is collected from the phloem or bast surrounding the stem of certain dicotyledonous plants. It provides strength to the stem and supports the conductive cells of the phloem. Bast fibres are usually characterized by fineness and flexibility, and they are also known as "soft" fibres, distinguishing them from the coarser, less flexible fibres of the leaf fibre, or "hard" fibre, group.

Bast fibres are used in a variety of applications, including high-quality textiles, ropes, yarn, paper, composite materials, and burlap. They 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, and more.

Some of the plants that have been used for bast fibre include flax, hemp, jute, kenaf, kudzu, linden, milkweed, nettle, okra, paper mulberry, ramie, and roselle hemp. The composition of bast fibres varies between plants, but they are mainly composed of cellulose, hemicellulose, lignin, and pectin.

Bast fibres are a sustainable alternative to cotton, the fashion industrys leading plant-based fibre, as they offer an eco-friendly, regenerative solution that decreases the need for irrigation, fertilizers, and pesticides to produce the fabrics that we wear. Plants that produce bast fibres tend to require less irrigation and other inputs than cotton, making them a more sustainable option.