DON'T TAKE OUR WORD FOR IT Internal testing by the German Triathlon Federation (DTU) shows that this is the fastest swimming tri suit they've ever tested. Then Castelli adds the aero speed on the bike and run. You'll get to the finish line faster. The secret is in Castelli's unique engineered stretch woven fabric. Rather than stitching together different fabrics for different functions, we actually change the texture and performance of the fabric in the areas where it needs to perform different functions. This is most evident at the leg opening, where a gripper elastic is woven into the inside of the fabric to hold the leg in place, while the rest of the leg is smooth for speed in the water. This technique allows the lower portion of the suit to be made from a single piece of fabric. And the suit tests fast in the wind tunnel on the bike as well. But the DTU also wanted extra cooling on the upper body for the run, so there's a different fabric on the chest and back that stays cooler and wicks away moisture. This suit was developed for pure speed, and it delivers in every discipline.