Slippage occurs when frictional force is exceeded at contact points. The condition for slippage is tan(β) ≥ Coefficient of Friction. During the slippage phase the interlocking angle remains unchanged and is equal to the value at the start of slippage. The path lengths LBC and LAB change mainly because of loop deformation. For modelling loop deformation mechanics with yarn slippage, the unknown variables that will have to be estimated prior to using the elastica model are the curvature pc(0), the external force FX acting at B of loop part BC and the length LBC.Seam slippage can also occur because of the stress location of a garment, thread type and properties, sewing needle, stitch type, stitch density, seam type, and sewing machine condition. The explanations are similar to those given for seam strength, which were discussed in the section on seam strength. As in the case of the effect of sewing thread on seam strength, lightweight fabric should be sewn with finer threads. Regarding the seam type, Morris and Brain found that lockstitch and chain-stitch seams produce similar effects but safety stitching, with needles closely spaced, may increase seam slippage.