First let us explain the numbers. What do numbers like 5/4/3 and 4/3 represent when we are talking about wetsuits? These numbers give us the thickness of the neoprene from which the wetsuit is made. This thickness is given in millimeters. So basically in a case of a 5/4/3 wetsuit this means that this wetsuit is made using three differently thick sheets of neoprene. One is 5 millimeters thick, the second is 4 millimeters and the third 3 millimeters.
Why not just make the whole wetsuit 5 millimeters thick? Wouldn’t it be warmer?
Well yeah, it would be warmer, but it would also be much less flexible and much harder to wear. What manufacturers do is they use thinner neoprene on places where you need more flexibility. Places like your shoulders, your arms, under your armpits, between your legs and behind your knees. Usually the thickest neoprene is covering your body and your legs and other mentioned places are made out of 4 millimeters or 3 millimeters thick neoprene. Which one is used where also depends on each model.
When to wear a 5/4/3 and when 4/3?
It’s hard to give a straight answer to this because there are many factors that influence the feeling of cold and consequently what wetsuit to wear. We tried to explain this in our wetsuit thickness and water temperature guide and chart. But in short, a 5/4/3 wetsuit is used when water temps drop below 54F (12C). Of course at that temperature only a wetsuit will not be enough. You will also need booties, maybe even gloves and a hoodie.