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A drysuit is usually used in water with temperatures around freezing point. It's called a drysuit because your body will stay dry underneath the suit. Seals at the neck and wrist prevent water from coming in. The zipper is also waterproof and the shoes are attached to the suit. Underneath the suit you can wear an isolating undersuit that works the same as thermal underwear. It will keep you warmer for longer. A drysuit doesn't prevent you from getting cold at all, but it wil certainly give you quite an amount of time to scuba dive comfortabely in cold water.

Both fabric and neoprene drysuits have advantages and disadvantage. A fabric drysuit is more adaptable to varying water temperatures because different garments can be layered underneath. However, they are quite bulky and some people need some practising with such a drysuit before the can dive with a suit like that. If you get a leak in a drysuit and it floods, it loses nearly all of its insulating properties. Neoprene drysuits are comparatively streamlined like wetsuits, but it's not easy for an undersuit to be layered underneath and are thus less adaptable to varying temperatures. An advantage of this design is that even it if floods completely, it essentially becomes a wetsuit and will still provide some insulation.