Keeping warm - Dry suits

Which is the right dry suit for me? The UK has some cold water. In summer you may get away with a semi-dry suit but come winter most divers will be wearing a dry suit. Dry suits as the name suggests does not (or should not) allow any water into the suit. The air in the suit is a good thermal insulator and with the right under-suit (layers) should keep you warm on any dive in the UK. When considering buying a dry suit we have some choices:-
1) Neoprene dry suit (compressed and un-compressed)

2) Membrane dry suit (trilaminate / polyester)

Then we have the choice of rear zip (across the back of your shoulders) front zip (from shoulder to hip).
Then we have the choice of the material the wrist and neck seals are made of; latex rubber or neoprene.
Then we have a choice of air dumps.
Lots of choices!
Advantages and disadvantages of neoprene dry suits:-
Warmer and more flexible
Need more weight and if not compressed neoprene will compress at depth
Advantages and disadvantages of membrane dry suits:-
need less weight than neoprene suits
membrane material does not flex so sizing (especially in body hoop) more important, not as warm as neoprene suits

Braces are a good feature to look for so when on surface you can unzip and cool down.
When buying a dry suit you will need to get the right size boots - consider you may put a couple of pairs socks on!
Rear or front zip - rear zip you may need help to fasten / un-fasten the zip; front zip your may need to be flexible to get your head in!
Some modern membrane suits are now being designed with a concertina feature (extra material in the middle / waist area) that allow more flexibility when bending over to say put your fins on.
To stop the water entering the suit a dry suit has a neck seal and wrist seals. These can be either latex rubber or neoprene both work well and often this is down to personal preference. Latex rubber seals can be carefully trimmed to give better fit (be careful - too much and they may leak!). In time seals will stretch, split but can be replaced with new ones as can boots if they start to leak / wear.
On a dry suit in the centre of chest area is the low pressure inflator valve. This is connected via a hose to the low pressure port on the first stage of your regulator. If buying a new suit the hose should come with the suit, check when buying second-user suits. On the sleeve there is at least one air dump valve, this can be an automatic should valve (that you open / close to adjust the amount of air released) and or a cuff dump where you need to rise the arm to a high point to release air.
All these features on a dry suit work well the choices are mostly down to personal choices and costs.
When buying second-user dry suits getting the right size is very important (you can always change the boots - approx. 80). Another consideration is the amount of dives it has done and how long it has been in storage, too much of either of these can cause problems.
As at the time of writing this article a new dry suit with an under-suit starts at about 399 top of the range suits can cost up to 2000!