The Ultra Rebound Speed Bag is based on the very same principle as Galileo's pendulum device. An additional layer of leather at the base of the speed bag provides the increased weight distribution for a faster, truer rebound off the platform and will challenge even the most seasoned speed bag practitioners. Available in Extra Small (5" x 8"), Small (6" x 9"), Medium (7" x 10"). FeaturesThe Ultra Rebound Speed Bag is based on the very same principle as Galileo's pendulum device. An additional layer of leather at the base of the speed bag provides the increased weight distribution for a faster, truer rebound off the platform and will challenge even the most seasoned speed bag practitioners. Available in Extra Small (5" x 8"), Small (6" x 9"), Medium (7" x 10").