Introducing the Sumo Sacs, the most flexible, puncture-resistant ballast bags available today. Sumo Sacs are made with a sandwiched, woven polyester core and have internally glued and taped seams for a nearly indestructible bag. The sandwich construction keeps them thin, so they are easy to fold up and store when not in use. We spent a lot of time measuring different boats to make sure that these square bags will fit anywhere on any boat.