In case different materials for warp and weft are used, then both code letters have to be used. The first letter will stand for the warp (longitudinal) material and the second letter for the weft (transverse) material. In case weft or warp are made of different materials, then the letter code for the material that is mainly being used for the tensile strength stands in front, separated by a "/". Letters for non-carrying material are separated from the warp by "-".