The mechanical properties of fabric longitudinal extension and compression, sheer and bending have an important influence on the performance of fabrics during tailoring and also on the performance of garments during use. Fabrics are overfed or underfed in tailoring during the sewing operations in such a way that longitudinal compression and extension are allowed in the fabric plane in order to produce the three-dimensional shape or fullness of the garment. Fabric buckling or puckering at the seams should not occur, or if it does, should be removed during subsequent steam pressing operations. An experiment is described to measure the maximum limit of overfeeding that is possible during seaming without the subsequent formation seam puckers. The relationships are studied between the maximum degree of overfeed, the bias angle between the feed direction and the fabric warp or weft, fibre type and fabric mechanical properties, especially fabric formability defined as the product of fabric bending rigidity and fabric longitudinal compressibility. Actual measurements during tailoring of the degree of overfeeding and the longitudinal tensile and compressive strains for various seams in men’s tailored jackets show reasonable agreement with the maximum limits of overfeeding predicted from the experimental measurements. The benefits of seaming on the bias and of steam pressing after seaming can be quantitatively determined for areas of the garment around the collar, shoulder and upper sleeve where a high degree of fullness and overfeed are required. When fabrics are extended or compressed longitudinally at a bias angle to the warp or weft direction during seaming in order to produce garment fullness, the warp and weft threads are rotated relative to each other in such a way that a local shear deformation is applied to the fabric and adjacent to the seam-line. Measurements are reported of the variations in the local shear angle along the should seam-line of a men’s jacket and the measured values are related to the high degree of overfeed required in the bias direction in this area of the garment. Finally, hygral expansion measurements for wool fabrics and yarns unraveled from the fabrics are measured and are compared for six different wool fabrics. The garment appearance, particularly at places where fabrics are joined together either by seaming or by fusing, may deteriorate greatly during wear if fabric hygral expansion is excessive.