These high quality ropes are endorsed by the National Double Dutch League. They are the same ropes used by Go Fish in the Gotta Move! VBS music videos and all official double dutch competitions. 14' ropes work great with both one or two jumpers.
We can say from personal experience that there is a big difference between these ropes and the rope found at hardware stores. Several sets may be helpful to engage as many children as possible during the 3D rotation.
Make sure to watch the double dutch instructional video on the 3D: Double Dutch & Dance DVD.