Twisted pair cable, such as 3M 3644 Series, provides a good, low-cost solution with good balance. Twisted pair cable is flexible, and capable of medium to long runs depending upon the application’s skew budget. For the lowest skew, 3M recommends grouping skew-dependent pairs together in the same ring to minimize skew between pairs. Ground or terminate unused conductors, or both if your system design permits, but do not allow them to float.