A 4mm wetsuit is the most allround thickness that can be used in all seasons except for the winter. So if you're a nice-weather surfer and aren't planning to surf in cold conditions the 4mm will be a perfect option if you're looking for just 1 wetsuit. Of course there are a lot of features in a wetsuit that can make a lot of difference in warmth. But regularly the 4mm wetsuit is the most populair thickness.
