Zoot's Z Force 4.0 WetZoot has a Zero Water Friction Free Neck Panel that eliminates neck constriction to create an extremely low profile neck seal. This suit sits flat against the neck to limit water entry and stop chafing. The 4.0 has has an Optimal Kick Design which is leg patterning that makes a wetsuit work with your anatomy rather than fight it. Benefits include increased kick velocity, frequency, and efficiency. The suit also has a DORSALflex zipper - 2mm of neoprene around the back zipper gives better stretch for improved lung expansion. No more traditional wetsuit restrictive fit.