The FitBALL Resistance Band 50-Yard Roll from Ball Dynamics is a great resource for exercise and fitness classes, or for the avid fitness guru. These stretch resistance bands are made of natural rubber and are a great way to increase muscle tone and strength. The blue color follows Ball Dynamics color-coded resistance system. An entire collection of 50-Yard Roll Resistance Bands are also available in 5 different resistance levels from Ball Dynamics.