I know the attributes of Gore Windstopper but don't understand the usefullness as a bag shell, considering the redundancy when using with a tent, bivy, etc. Can someone enlighten me?

For me, it functions as a strongly water-resistant shell. I have been directly rained on in a Grand Canyon thunderstorm and had no wetting of the down. In a recent kayak trip, the first night was rainy and my son's Rainshadow tent wasn't pitched quite correctly with the result that we got a puddle on the tent floor on my side. There was some dampness but not what it would have been with any other fabric.

I wouldn't rely on it as waterproof because of the needle holes in the seams, but it is extremely water resistant.

I'm considering a WM Kodiak GWS for my winters in the Smokies. The max temp I'd use it at would be about 25dF so rain is unlikely but snow showers would be probable. I think the GWS with a sil/ponch/tarp would be a great combo but some folks don't think so. I've been using a Versalite with a bivy but I'm wanting to try my new idea. Folks, encourage or discourage, but please speak out!

If the Goretex bag was lighter than an equivalent bag plus a bivy, I'd say it make sense. It certainly would work and the colder the better.

I would think the biggest issue would be if semi-slush that was close to the melting point built up on the bag and then slowly melted, you might risk some penetration through the thread holes. But in any case it would not be bad enough to be a trip ender. The lower the temperature, the less likely there will be much melting at the surface of the bag.

I would also expect it to perform admirably with splash and overspray coming in from the side of a tarp.

Gore prevents any seller of Windstopper to even whisper anything about water resistance -- and it certainly can't be guaranteed to be water proof. However, what it is, is Goretex and it has all the usual properties of Goretex which includes resistance to water penetration. It is just thinner than what is used for rain wear and not seam sealed, etc.

What I have on my Feathered Friends bag is Gore Dry Loft -- which I believe to be about the same thing. I'm not up-to-date on all the latest versions of Gore products and how that relates to Gore's current marketing lingo. If someone knows differently, I would hope they chime in.

In certain situations, with out the use of a bivy, my Gore Dryloft (GDL) shell on my Puma has provided protection from moisture.

Sleeping in an enclosed single wall tent like a Betamid or Silshelter, where condensation forms on the interior (and before it freezes), the GDL keeps the down dry should my bag be touching the sides of the Betamid.

When sleeping under a tarp in stormy weather, invariably there will be spindrift snow blow in the ends - assuming of course there is snow on the ground or on the trees above and the ends of your tarp are open. Snow blows off the trees and swirls around, even in well protected forested areas. This situation is even more pronounced if there is actually snow falling during a storm. In this situation the GDL, again adds that extra level of protection over a simple DWR shell.

In milder conditions the GDL on my MEC Emperor Penguin overbag works in the same manner with my first example above. When under a tarp in the rain, it certainly adds some protection from splashes of rain that find there way into the ends or under the sides of an open tarp.

I would take a look at microfiber shells. I've been using the Apache SMF for several years now, and very happy with its performance. The problem with GWS is it's not very breathable and that alone may cause the insulation to get wet. In the winter I've not had problems keeping the bag dry from outside. On extended winter trips my issue has always been trying to keep the bag dry from perspiration. The microfiber shell offers good weather resistence but at the same time breathes very well. One other issue I have with GWS shells: When stuffing the bag you have to turn it inside out first or you will be wrestling with a balloon. I hope this helps.

Those GWS type shells are a real hassle to stuff.

One thing I've noticed in the past, is that in very cold weather, I'd often get frost build up between my sleeping bag and sleeping pad.

With a better sleeping pad and a sleeping bag with a wpb shell, I'm not seeing this anymore. I wonder where the moisture is ending up.