Our cotton sash cord features a braided cotton jacket over a synthetic core for added strength and to reduce stretch. Overall this is a good mix to produce a sash cord that is soft, flexible, easy on the hands, and keeps stays round under load.
The particular braiding pattern makes it easy to tie knots when fastening the sash weights as well as to flow smoothly through the sash pulley during use.
Cotton sash cord has good resistance to sunlight and can even be used as a good general-purpose rope.
Estimate your needs
Measure the window's overall height from the bottom of the window jamb to the top of the Sash Pulley.
Add another foot to account for attaching one end to the window sash itself and for tying knots on the other end to the sash weights.
Double that measurement, and you will have enough for both sides of the window.