Specially blended filler mix of sanitized synthetic and natural fibers provide resilient shock absorbency Premium synthetic leather with reinforced webbing along with superior heavy bag construction increases durability and functionality Heavy duty nylon straps provide security and safety *ZIPPER - Our heavy bags are made with a locking zipper to keep the bag from opening; During the manufacturing process, we want the stuffing to be appropriately enclosed within the bag; By breaking off the zipper, our heavy bags stay permanently locked and free from unzipping, keeping the overall bag intact and responsive when used for physical activity