Originally Posted by
BackPacker
You are right that the cold is the major issue here. So underneath the dry suit you have to wear a few layers of clothing that provide insulation. Divers use special "bear suits" which are coveralls made of fleece or something similar, but for aviation emergency use you can probably get by with normal pants (jeans possibly), a t-shirt and a sweater or something like that. The main issue is that you stay dry, because air is a much better insulator than water.
Just a bit more context. I was doing rescue duty at our sailing lake one winter day and decided to 'check out' my dry suit. We had to break ice up around the docks and slipways so the surface water temperature was likely just above 0. I was wearing normal jeans, a warm shirt and medium weight fleece, and winter weight wool socks under the dry suit and insulated sailing gloves on the hands.
I jumped in (but did not put my head underwater) and paddled around for about 15 minutes. My hands where quite cold, but still usable. My neck started to hurt from cold at the point just above the neck seal but still in and out of the water. The rest of me remained fine.
So on a cool day, you probably would be wearing about the right amount of clothing. The problem is on a hot April day when the cockpit is very warm but the water is bloody cold.