The basis of Xtenex shoelaces is the elasticity involved. The x400 series shoelaces are especially made to accommodate the size of the eyelets particular to work or hiking boots.
The bootlaces consist of a line of knots which are held in place even when a lace is cut. When stretched out, the knots are also stretched for easy lacing. When the laces are in place, the knots are there to assure a secure fit.
These bootlaces will expand if the foot should swell due to exertion or over extension of muscles.