Every harness in our Z Series are equipped with "bungee cord-like" elastic rubber straps. On top of that, the Convertible Z comes with the following features: Convertible Hybrid Design - Hybrid between "head-in" and "step-in" harness. Fastener Neck Closure - easy adjustment of the neck size for a more secure fit, something you don't find with traditional head-in harnesses. Shock Absorbing Design - cushions and softens the sudden shock when your pup pulls so it's not so hard on your arms. Flexible Body Frame - contours to your pup's body shape and moves around as your pup moves, creating maximum comfort. Note: The Convertible Z is a great option for excited pups that constantly pulls or if you're unsure about choosing a "head-in" or "step-in" harness.