Fibre size often referred to as fineness, is one of the most important properties of fibres. It is usually specified in terms of diameter or linear density. The size of natural fibres is often given as a diameter in micrometre units. It reflects the average width along the length of the fibre. The sizes of silk and manufactured fibres are usually given in denier or tex units, which specify the linear density based on weight per unit length. Denier is the weight in grams of 9000 m of a fibre; tex is the weight in grams of 1000 m of a fibres Tex is one-ninth of 1 denier. See also Fibre Length, Fibre Morphology overview, and Fibre crimp.