On June 21st, 2010 USA Triathlon adopted a new regulation concerning allowable thickness for wetsuits. “Effective January 1, 2013 any swimmer wearing a wetsuit with a thickness measured in any part greater than five millimeters shall be disqualified.”
USA Triathlon (USAT) is the governing body for triathlons in the U.S. and most of the advertised triathlon races are USAT sanctioned events.
I think this rule will be a non-issue for most people that have purchased a wetsuit in the last couple of years. I bought an new Xterra Vortex 3 Wetsuit in February 2010 and the thickness of that suit is between 3-5mm. This new rule also falls in line with the guidelines already in place by the International Triathlon Union (ITU). If you have a wetsuit that is too thick, the new rule does not go into effect till 2013 giving you plenty of time to purchase a new one.
Read the full article at usatriathlon.org