Linen is a bast fiber. Flax fibers vary in length from about 25 to 150 mm (1 to 6 in) and average 12-16 micrometers in diameter. There are two varieties: shorter tow fibers used for coarser fabrics and longer line fibers used for finer fabrics. Flax fibers can usually be identified by their “nodes” which add to the flexibility and texture of the fabric. The cross-section of the linen fiber is made up of irregular polygonal shapes which contribute to the coarse texture of the fabric. Linen fabric feels cool to the touch. It is smooth, making the finished fabric lint-free, and gets softer the more it is washed. Linen has poor elasticity and does not spring back readily, explaining why it wrinkles so easily. Linen fabrics have a high natural luster; their natural color ranges between shades of ivory, ecru, tan, or grey. Pure white linen is created by heavy bleaching. Linen fabric typically varies somewhat in thickness and is crisp and textured, but it can in some cases feel stiff and rough, and in other cases feel soft and smooth. When properly prepared, linen fabric has the ability to absorb and lose water rapidly. Linen can absorb a fair amount of moisture without feeling unpleasantly damp to the skin, unlike cotton. Linen is a very durable, strong fabric, and one of the few that are stronger wet than dry. The fibers do not stretch, and are resistant to damage from abrasion.