Some knitted fabrics are under free state, and wraps sometimes appear on the edges. This phenomenon is generally called curling. It is caused by the fact that the bent line segment in the coil has internal stress to straighten the line segment. Inside the knitted fabric, the coils are interconnected, and there are mutual restrictions. The bending cannot be restored. However, on the edge of some knitted fabrics, there is no constraint on a short section of the loop, and the yarn tries to straighten the curl caused.

 In the organizational structure of hemming and knitted fabrics, linear density, yarn elasticity, coil length and twist are all related.