A swimskin is a one-piece suit that is placed above a tri-suit in a non-wetsuit swim. It is worn to increase hydrodynamic gains by reducing the friction between body and water due to the smooth surface of the suit and its snug nature on the body. Due to the tight – yet hopefully unrestrictive – fit, a swimskin will also improve the alignment of your body in the water.
A swimskin will often be seen where the water temperature is warmer than 24°C for an 3.8km Ironman distance race – see the Ironman World Championships in Kona, Hawaii – and where wetsuit use is forbidden (but each race organiser and federation can have different rulings on wetsuit legality and water temperatures, so check before race day).
A swimskin is thinner than a wetsuit and will only offer a little added buoyancy or warmth. It will often be sleeveless or will have short sleeves on the arms, and will reach down to the knees on the legs. The zipper will be located on the rear to further reduce frontal drag.
How much faster will a swimskin make you?
So what are the benefits? In a swimming pool test by the U.S. Olympic swim team, swimskims saved an average of just over 2secs per 100 yards (91m) when compared to a typical training suit. That’s a 40sec saving over an Ironman 70.3 swim of 1.9km and around 1:20mins for a full-distance 3.8km swim (minus the time it takes to remove it in transition one), but much of the gains will depend on the swimmer’s ability.