Went out in 13 Celsius, never felt cold, even when duck diving, amazing warmth from the 4/3 Defender, unlike some other front zip wetsuit a very popular brand, I find that water doesn't "Dam" in my lower back, which makes me feel cold after awhile, not to mention annoying. If on occasions, water does flush down into to the lower back, after a serious duck dive getting under a monster, it doesn't stay there and the wetsuit warms up again fairly quickly, even sometimes when paddling, I can feel the wetsuit reflecting my body heat, very warm...nooice!! a solid product, very happy, I feel no FEAR, when looking out across the ocean on a frigid winters morn.