This new bag from Everlast features a water core. The water core gives the bag a lifelike feel as opposed to regular foam filled bags. The water is contained inside the bag in a radio frequency welded urethane bladder that is easy to fill and resists leaks and bulges at the seams. the outside of the bag is made with a polyurethane foam layer that will absorb the vibrations from your punches and kicks keeping you cofmortable and reducing wear and tear on the bag. this is a great bag for users of any skill.