Polycord is a very popular choice among FRC teams. Do a google search or a forum search to find more information to help you out. If you need help on the easiest way to join Polycord without any special tooling, PM me.
Note that Polycord is a brand name, and these cords you see on most intakes are known as urethane belts.
We source our cord from
McMaster-Carr.