Abstract: A flat woven, pin seamed, papermakers' fabric, comprising primary warp monofilament yarns, primary weft monofilament yarns and secondary weft monofilament yarns located between and adjacent to the primary weft yarns. The secondary weft yarns are located beneath, and in contact with, the primary warp. The thickness and width of the secondary weft yarns are chosen at the weaving stage so as to control finished fabric air permeability and increase the paper side surface contact area. The fabrics are of a lower caliper, and provide increased cross direction stiffness at lower yarn counts. Formation of the pintle receiving loop yarns in a low marking woven back pin seam, or of a streamline seam, is also facilitated, without compromising fabric properties, by selection of the appropriate dimensions of the secondary weft yarns.