making a “vapor liner” to layer with a down bag/quilt in the winter — will it work?

[Jordo _99]

Has anybody used a 3-season down sleep system in the winter with (what I'm calling) a "vapor barrier"…something like this:

vapor barrier has a wicking inner shell and the outer shell is a reflective, waterproof barrier like mylar…it would be filled with insulation that retains heat well when wet(likely synthetic or possibly wool)

…in an ideal situation (if this worked)…the down bag/quilt would stay dry while the "vapor barrier" would absorb the condensation building up and maximize heat retention.

…it's not very practical for multi-night use if the vapor barrier isn't dried out during the day…also I'm not sure the down would stay dry…anybody try this before?

[Tom Lyons]

It's quite common, particularly in cold weather sleeping situations.

The "wicking" part is your baselayer long underwear.
The "Vapor Barrier Layer" is usually a bag that is waterproof, and non-breathable, and can fit in the sleeping bag with you.

Your body and baselayer inside the VBL creates a "micro climate" which keeps you warmer and stops any body moisture from penetrating into the down insulation of the bag, keeping it dry and able to fully loft for better insulation performance.

If you want to shield the down insulation from external moisture, you can then put a waterproof bag around your down sleeping bag on the outside, without fear of wetting out the bag from your body moisture inside, because you are using the VBL.

There is actually a company which makes VBL clothing with a fabric flocking inside the non-breathable VBL layer, and it looks like long underwear, and has the advantage of not being restrictive of your arms and legs. It wears just like long underwear.
It's quite expensive, and heavy.

Your cheapest and easiest bet to get to where you are going, is to use a good wicking baselayer, and use an Adventure Medical Kit SOL emergency bivy bag that costs $16 and weighs about 3.5 ounces as your VBL bag.

You have to get a "feel" for using this VBL concept because it is so much warmer that you can easily sweat too much inside the VBL.
So, you have to pay attention to your body temp, and be able to layer off insulation or layer on insulation, depending on the need.
After a while, you get to know what is going to be needed in various situations, and it becomes a routine activity to dress for your need for the temps and VBL.
Like anything, it requires a little practice to get to where it feels like "2nd nature".

Regarding multi-day outings, that is where this system actually shines the most, because it keeps the down from accumulating moisture over several days time which can lead to insulation collapse. And insulation collapse can be dangerous.
The VBL is much easier to dry out on a daily basis because all the moisture is on the surface inside the VBL, or in the wicking baselayer, both of which dry quickly.

[Jeff McWilliams]

One thing that I haven't quite wrapped my head around is this:

If I'm wearing a wicking layer, and using a VBL plus a bag, then I can't add, say, a down puffy as an extra insulating layer, can I?

If temps drop, any additional layering that I do has to happen outside the VBL, correct? This means I can't easily use additional clothing to layer up, like I could if I'm without a VBL.

I suppose I could spread out my down puffy between the VBL and my bag, or on top of my bag, but it would be non-optimal. If I toss and turn at night, it's likely to fall off or get shifted around.

Any thoughts on this?

Thanks

[Tim Marshall]

if you use VBL clothes you can add your insulating clothes over them. IF you use a VBL liner (or VBL quilt is those existed ;) you can wear your insulation with your WPB rain gear over it inside the VBL. Both options work.

-Tim

[Here There]

"you can wear your insulation with your WPB rain gear over it inside the VBL"

Tim, do you mean: WPB clothing->puffy clothing->VBL layer?

The bit I quoted sounds like you're saying: puffy clothing->WPB clothing->VBL layer, which wets out the puffy clothing.

I first started using rain gear as VBL (before I had WPB gear) before I'd ever heard the term "VBL" and found through trial and error that the rain gear needs to go under puffy layers or they'll wet out.

-David

[Tim Marshall]

If the raingear is breathable (wpb) then it can go over the puffys and still pass vapor unless you get way too hot then it can't move it fast enough. If you don't sweat then your body vapor passes through puffy, through wpb and is trapped between vbl and wpb. The easiest is just vb clothes under everything then I use the epiphany because it's lighter and don't really need it for vb

-Tim

[Jerry Adams]

On the Stephenson website they say that inside the VBL, the humidity gets high, which cuts perspiration.

If the puffy was inside the VBL, it would be in the high humidity zone, so it would get wet?

I think you want nothing inside VBL. Or thin base layer if that's what you need to be comfortable.

Off that subject a bit, I made VBL clothing out of "fuzzy stuff" from Stephenson which I used as base layer. I thought that regular base layer was just as warm so I ditched the VBL.

I think VBL is only good when you are very cold for extended periods – like on an arctic expedition which is the example Stephenson uses

[Here There]

I guess I give off a lot of moisture because even "breathable" rain gear acts as a VBL for me, soaking any layers underneath. So the moral is, experiment close to home!

-David

[Jeff J]

In response to the "I can't wear an extra layer under the vapor barrier?" question, the answer is dependent on the insulation type, of course. Down is no good inside a vb bag as you know. Synthetic might hang in there. Fleece will hold up and keep you warm though, at the cost of more weight per warmth. Since in the winter, one carries more gear, clothing, and weight, I think it makes sense to wear fleece inside and lay the puffy outside the vb.

Having multiple types of insulation in the winter is insurance anyway.

-Jeff

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