We zip up the O'Neill Psycho-TechWetsuit before hitting the water to ensure we're warm and covered for the duration of the session. The 4/3+ thickness lends itself well in cool to cold water thanks to the extra 0. 5 millimeters of insulation, and it can even fluctuate into warmer temperatures with ease. This versatility is provided by the combination of the TechnoButter 4 and Technobutter Firewall fabrics that combine to keep water out, move with you, and trap air for impressive warmth.