The Mystic wind barrier kills the windchill. Most wetsuits are made out of double lined neoprene combined with some Single lined neoprene panels. This single lined neoprene is windchill proof, but the double lined neoprene isn't and if the wind is strong and cold you will feel this on your skin.
The very light wind barrier is 100% wind-proof and therefore your whole upper-body is protected against the wind while wearing this!
A must-have during winter!