Essentially all wetsuits work on the same principle; they are designed to trap a thin layer of water against your skin which your body warms and in turn keeps your body warm. The neoprene used insulates your body against the cold water which is why a thicker suit is warmer.
Freediving suit design differs from other sports such as surfing or scuba diving. As freediving suits are designed to be worn all day (the length of time a freediver spends in the water is much longer than most other pursuits) they must be very warm and very comfortable.
To facilitate this all freediving suits share several similar design features:
LOW-DENSITY NEOPRENE: This is the main reason why freediving suits are so much more comfortable than others. The low density makes them extremely flexible and light to wear.
TWO-PIECE: All freedivng suits consist of either a long-john or trousers and a jacket with attached hood. This means that the suit does not need zips to get on and, in the long-john option, there is twice as much rubber over your chest where it is most needed. It is also great for young divers as there is much more room for growth than in a one piece.
NO ZIPS: Freediving suits have no zips for two main reasons: Zips let water into the suit and they don't stretch. Obviously these contradict the two main goals of being warm and comfortable so we can't have them.
OPEN-CELL INTERIOR: For a suit to be truly comfortable there must be no linings or seams rubbing on your body. Freediving suits have what's called an open-cell interior which means it is raw neoprene against your skin. Not only does this make the suit infinitely more comfortable it also makes the suit stick to your skin inhibiting water movement making the suit warmer. The flipside of this is it makes the suits difficult to get into. To get around this you fill freediving suits with a soapy water mixture before donning.
So this is what all suits have in common so what are the differences?
Mainly two things, the quality of the neoprene and the cut. All neoprenes are not created equal. The better the neoprene, the stretchier and more comfortable the suit will be. This can create a compromise with how long the suit will last although the latest neoprenes are very stretchy and comfortable but also have a very high elastic memory which greatly enhances suit life.
Each brand of suit will also have a slightly different cut making them more or less suitable for individual body types. Once again it is important to try as many suits as you can to decide which one best suits you or ask for advice from the vendor before purchase.
All spearfishing suits will come with a loading pad in the middle of the chest to load your speargun against. Better suits will also have some reinforcing around the knees and maybe elbows as well. Bear in mind that reinforced padding will not be particularly stretchy so there is a bit of a compromise between comfort and durability. The material from the top of the knee down is where most wear occurs and does not need to be very flexible as the large panel along the top of the thigh will provide enough stretch for comfort.
Generally a 5mm suit will get you through the whole year in New Zealand but very active spearos will also have a 3mm for the middle of summer and a 7mm jacket at least for the winter.
Most specialist spearfishing suits will come in camo. Whether or not the camo makes much of a difference is up for discussion (read here for more about Camo and Cover) and should be the last thing you consider when buying a suit but for New Zealand conditions look for dark reddy, browns to match our kelpy reefs.
Divers should consider boots and gloves as "consumables". There are a few things however you should watch out for. Do not choose boots with a stitched seam running along the heel as they will inevitably cause blisters. Do not get thick, neoprene gloves (unless its so cold you simply must have them) as the dexterity of an amara style glove is much better.
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