This 3 mm-thick neoprene vest with a built-in thermal hood can be worn underneath a regular wetsuit to make cold water swimming safer and more comfortable. The thermal lining provides an extra layer of warmth, preventing the loss of body heat during exercise. The neck cover also provides thermal insulation and minimizes the body's contact with cold water.  This product's pattern fits tightly to your head so that it won't move around while you're swimming in open water. Its soft lining also makes it more comfortable. With its Open Cell material, the vest fits perfectly to your body, without moving around or interfering with your wetsuit. The neck cover prevents water from getting into the chest area, helping to maintain body temperature.