Static grass consists of man-made fibres selected for their ability to hold a static electric charge. They are usually a blend of coloured nylon, rayon, or polyester fibres that are used to more realistically replicate grass on a modeller's layout. The fibres are usually sold by weight in 2, 4, 6, 10 and 12 millimetre lengths, although fibres can be found from as little as 0.5 mm in length.