What Are Bast Fibers? Bast fibers, also commonly referred to as skin fibers, are natural plant-based fibers that grow within the stems of certain plants. Located in the inner bark, or phloem layer, of the stalk, these fibers can reach several feet in length. As one of the major natural vegetable fiber resources in the world, bast fiber plays an important role in the textile industry. Most of the important bast fibers are obtained from plants cultivated in agriculture, includi