Swimming

Hmm I have just found an answer:

A wetsuit specifically designed for swimming (usually sold as a triathlon wetsuit) provides significant advantages over a general wetsuit (eg a surfing wetsuit). Swimming wetsuits are more flexible, particularly in the shoulders, have a slick external layer (reducing drag) and manufacturers design the buoyancy of the suit with swimming in mind ie your legs aren't so high in the water you're kicking in thin air.
Swimming suits generally have sections of thinner neoprene (usually 2-3mm) in particular areas around joints such as shoulders and knees whereas the rest of the suit may well be made mostly of neoprene up to 5mm thick (the maximum allowed under International Triathlon race rules). Thicker wetsuits provide increased buoyancy although they can be awkward to swim in (if thicker than 5mm) but will keep you warmer. Surf wetsuits are frequently hard to do freestyle in on the shoulders, and have legs so buoyant your feet are above the water so you can't kick in breaststroke.

from http://www.outdoorswimmingsociety.com/index.php?p=swimming_tips&s=outdoor

But I think that what it says about surfing wetsuits isn't entirely true: they *are *specifically designed to enable you to paddle easily, so allow for shoulder movement, and the thicker sections are usually only on the torso. Summer surfing suits are 2-3mm, so apparently the same thickness as swimming ones.
Dunno about the legs-buoyancy thing though.

Does anyone have any experience of the difference?