The wet suit works by trapping a layer of water between you and the suit. Your body warms the layer up and insulates you against the outside water. So when you jump into the water, you are going to feel a rush of cold water running into the suit - a bit of a shock sometimes, but it soon warms up.
As your body uses its own heat to warm the water up, it is vital the suit is not too baggy, as you would have to warm a larger water volume up and the water would also cool down as it is moves away from your body. The water layer in a wet-suit is a thin layer and you shouldn't feel the water "rushing" around
Therefore, the suit needs to fit tightly on your body - so don't buy a surface sport wetsuit (e.g. for wind-surfing), they are too baggy, are designed to be flexible for arm movements and have poor heat retention properties. Ensure you buy a scuba diving wet-suit, it will have seals around the neck, wrists and feet and will be a very snug fit. Don't be tempted to buy one at the supermarket, they are made from extremely low quality neoprene (usually synthetic neoprene), which doesn't have the warming qualities, is extremely more buoyant and is likely to rip easily.
Go to a shop and try a variety of them on. They should be quite difficult to get into, pulling the suit on, you may need somebody to even help you get them on initially (they do stretch over time). Once you've got the suit on, it should feel tight (without restricting your breathing), you should be able to move around in it - check your arm movement and try to squat.
In warm water, the shorty will cover your torso, shoulder and thighs. It will enough to keep your body warm and will keep you warm even on a deeper dive in warmer waters, where you might encounter a bit cooler water (thermocline) at depth.
It is in effect a shorty with full arm and leg length. There are a couple of key differences. Check the suit has a proper neck seal (usually a neoprene fold), wrist seals and layered foot seal (i.e. the inner seal goes into your boot and ankle seal - usually with a zipper goes over your boot). There will be different thickness available, most of the manufacturers have a thicker neoprene section around the mid-section, giving additional warmth for your kidneys and lower back.
In the past you would have bought a two layered system (considering of an armless dungaree type trousers) and a jacket (with a crotch strap). These types have effectively been superseded with a more practical solution. The newer system consist of a shorty and a full-body, allowing you to use the suit in a variety of conditions - shorty, full body and layered - effectively giving you three suits in one. The varieties are quite endless, best is to get advise from a number of different shops. Our favourite was the Oceanic Shadow - but it has been discontinued.
- the inner lining of the suit is made of tiny woven loops, giving a bit more space between the suit and the body - it gives a bit more warmth. Every few years it comes back into fashion.
Merino Wool - absorbs water and swells up. Merino wool can hold up to 30% more water , is very fine and soft against the skin (it doesn't scratch). In addition, it is exothermic (i.e. releases heat when it gets wet), which means it helps to warm you up and it doesn't compress as much as synthetic material (which cannot absorb water). Consequently, tests by the British Technology Group have shown that Merino Wool wetsuits offer an improved thermal efficiency of about 20% to 35%.
Titanium Lining is a reflective layer build into the neoprene suit. It reflects your body heat back into the suit, reducing heat loss and "reheating" the water.
Zips - there are metal and plastic zips. Metal zips last longer, but are prone to corrosion, while plastic zips are less robust but more comfortable and easier to maintain. Good suits will also have ankle zips, making them easier to get in an out.
Zip flap - a wet-suit should have a zip-flap, this is a piece of neoprene on the inside of the zip, that sits against your skin. This flap ensures your skin doesn't get trapped in your zip and is more comfortable to wear. In addition, you have a protective layer between you and the zip and therefore a better seal, which stops water from flooding through the zip.
Wet suit maintenance
Wet suits are very easily to maintain. After usage they should be washed out with fresh water and then allowed to dry naturally out of direct sunlight. If the suit starts to smell (there are two types of divers - divers who pee in their wetsuit and divers who lie), wash it out with a neoprene shampoo. If you don't have it on hand (in an emergency), we have used a mild washing up detergent - it works, but it takes ages to wash out the detergent (as it foams too much).