I plan on paddling 40 degree water. I have a dry top and dry pants. I have seen it posted that you should never wear your wet suit under you dry suite. Why? I understand you can work up a sweat, but would it not be a good insulator when water leaks in if I need to do a wet exit? I have mystery ware, a farmer john and a 3mm jacket.
You can
Dry top and pant combination (exactly what do you have?) is rarely actually dry if you end up taking a swim, or roll a lot, just not very wet if your dry separates are good enough. And you need a wind-proof shell over a wetsuit anyway because the wind tends to cut thru a wet wetsuit. The debate you probably encountered was about wearing wetsuit under a one-price, fully latex gaskets, (truly) drysuit. That can also be done but tends to be dastardly uncomfortable unless you can roll to cool off, and for some sitting in the sweat that’ll build up after some paddling in that combo gets cold in itself.
I think you’re confused
The rule is: Never wear your wetsuit OVER your drysuit. It can cause reverse osmosis and suck all the moisture right out of you… nasty chaffing too.
If you have a two-piece dry system, it would actually be a good idea to wear the wetsuit underneath. If you have drypants (instead of dry bibs) they will not seal well with the drytop. If you go in the water, it will leak, leaving you exposed to 40deg. water. The wetsuit will buy you some time to get out of the water, but I wouldn’t go far from shore without a full drysuit when paddling in 40deg. water.
Figured out the dry over wet thing
I will not be going far from shore and I will be paddling with others. I have tested the dry/wet system and the pant/top combo and it does leak a little but not bad in a normal wet exit re-entry. The cold water on my face is enough of a distraction to make me not notice the slight discomfort of the leaks………… usually taking a leak relieves the discomfort
fleece swim suit
I have been swimming 4 times already this year, and our water is 43, was probably colder before this. I wear fleece or polypro or wool (least prefered) under paddling gear that leaks. It’s trickle leaks, but I feel the cold water coming in, then it warms up in a minute. Seems to me that fleece under a windtight gear acts and feels a lot like a wetsuit. In moderate temperatures I have been continuing without changing to dry clothes.
I do stop, undo the leg closures and give standing water a chance to drain out. In the open water, you can’t do that. I think I’d get cold spots where water gathers inside the garmet without the chance to drain.
With your dry gear, you won’t be getting a ton of water, right? I’m thinking fleece will do you fine. But that could be just the booze talking. The folks in the CPA say “swim your gear”. Go for a swim and decide for yourself if the gear will work. Do it at the end of trip when you are going to be changing anyway. I have never taken that advice, I think because I swim so much as it is, 
I feel like I know what to expect.
~~Chip
Light top/Heavy bottom
Just a quick quip to follow up on good advice that’s already been said. Go with heavier fleece pants and polypro or synthetic long sleeve top under your dry garments. Your legs typcially are not doing a big aerobic work out, more isometric than anything else, while your upper torso is covering a range of motion and generating heat. Additionally your pfd is a very good insulator for your core.
If you are having an out of boat experience your torso is protected by your pfd, and your are bobbing around head up out of the water (I hope). This leaves your legs dangling in the cold h2o with the groin area being one of the body’s big heat zones. (no jokes Greyak). So a thicker lofting layer under the dry pants wil help.
Also depending on the drypant, if it has a wide neoprene waist band, it’s best seal is against skin. While not perfect it helps slow down the leaks. (aquatic not the ones you need to take) Just make sure that you tuck your poly pro top up above the waist band of the inner tunnel of your drytop or it’ll act as a wick pulling water up towrards your chest.
Have fun, stay dry, go paddle.
Marshall
www.the-river-connection.com