Drysuits are a must in many climates. I paddled on river and sea many a winter with a neoprene long john and dry cag and survived, but often cold especially when coming to land again. The first time I used a drysuit was just over 4 years ago and was instantly converted. Gone were the days of trying to get changed quickly as possible at the roadside, with only a towel around a shivering, blue skinned Scottish man with goose pimples the size of golf balls. But I use only in colder temperatures with the appropriate layers underneath. The most important thing to remember is that it is not the drysuit that keeps you warm, it merely keeps you dry.
There are several types of drysuit, with different types of neck and ankle seals and different types of foot or ankle seals.
The Yak drysuit here on the right is the type I prefer, latex seals around the neck and wrist cuffs, with a secondary seal in neoprene at the neck. Latex seals are much better for making a watertight seal and neoprene adds extra warmth as well as protecting the thinner latex underneath from abrasion.
Inner latex seal with the outer neoprene.
There are three types of ankle/foot seals. On the right is my preference with the socks made of the same waterproof material as the drysuit, the alternative being latex socks which I used on a pair of dry trousers many years ago but tore with great ease. Thirdly there ankle seals made of latex, better on dry trousers and not on drysuits.
There are also three different methods of entry in drysuits, The back entry with the zipper across the shoulders, the hinge zipper where the zipper goes around the waist and a diagonal zip over the chest. The back entry drysuits normally have internal braces which holds the drysuit in place when you open and remove the upper body for a breather,, not so with the other types. I have a hinge type but find the zip uncomfortable around my waist whilst in the kayak. The back entry is my prefered option here.
A necessity in winter, the drysuit keeps me dry, the layers underneath are equally important as they keep me warm. I often paddle in temperatures below -10C and use thin layers of different material which I take up in winter clothing.