Anyone here using a sleeping bag or quilt with cuben liner?

If your bag has a VBL liner, you can't really wear insulated clothing inside because it will get damp.

If you wear your insulated clothing inside your sleeping bag, you can extend down it's minimum comfort temperature or get by with a lighter sleeping bag

I always wear a layer of fleece with my VBLs. The dampness is no issue for me in my environments/conditions as the stuff dries within a few short minutes after exiting the bag.

I get by with a lighter bag by using a VBL. A couple ounces (at most) in VBL plastic allows me to save a ~pound of extra clothes.

Right now, for three seasons, I use mostly a Marmot Hydrogen sleeping bag. Mine weighs 23 oz. I carry the clothes I need to keep me comfortable outside my bag, and use them as needed inside my bag to keep me warm.

It's all about being reasonably comfortable, walking and sleeping. For me, I like being warm AND dry when possible. My "VBL" when needed is breathable rain gear. I'm going to feel drier at night without a VBL. But we all have different tolerances for discomfort so it's HYOH when it comes to gear selection.

It sounds to me like rusty b already has a fair amount of experience using a vapor barrier and he finds that it works for him. Responses so far seem to be missing the point of the original post.

I made a down quilt with a 0.33oz cuben shell and I've used it for trips longer than 3 days 6-7 times. I have never been able to completely eliminate sweating with venting and base-layer control, so, even near the low end of this quilt's temperature range the inner surface gets exposed to some perspiration, in my experience. I take cat baths with a microfiber washcloth before bed, and I wipe down the inside of the quilt in the morning and hang it up while I make breakfast and pack up. I haven't found yet that the cuben smells musty. The mylar surface is smooth and non-absorbent, so it's easy to wipe clean and it dries quickly.

Also, to answer a concern raised by Jerry, it's a popular myth that you can't use your warm clothes (even down-filled stuff) to improve the warmth of a sleeping bag or quilt with a vapor barrier. I read this frequently in threads about vapor barriers. The clothes just need to go on the outside. They loft better there, anyway. I put plastic snaps on my down jacket and pants and matching snaps on the outer shell of my quilt, to keep them from sliding off.

I made a quilt out of cuben fiber, very similar to Tim's Enlightened Eq. cuben quilt. I used it for 5 months on the PCT and for multiple (5?) week trips, and multiple (10?) weekend trips. I also used it for a few months in my dorm room when I started college. And I havent washed it at all. I know that is pretty gross, but honestly I have found that it airs out really well and I havent found a way that I feel comfortable to wash it. But I have heard that a wet rag works? Just thought I would throw my 2cents in…also, I have been comfortable in it down to 15 degrees while wearing my montbell alpine light jacket underneath it with little/no condensation, and also in my 70 degree dorm room, I just let my appendages stick out.

"it's a popular myth that you can't use your warm clothes (even down-filled stuff) to improve the warmth of a sleeping bag or quilt with a vapor barrier. I read this frequently in threads about vapor barriers. The clothes just need to go on the outside. They loft better there, anyway"

Ahhhh…that makes sense

By the way, it's not important to convince anyone that my way is right. Just throwing a bunch of ideas out there, people can try different things and use what works at any particular time…

But, you're wrong : )

The outside of the sleeping bag is designed to be the outside layer, so it's best being used in the that manner – it prevents wind from blowing through, prevents drafts from blowing in the sides, resists any water,…

My vest is designed to be an internal layer, so it's best being used in that manner

If you want to do VBL, better to have it as your clothing, rather than sleeping bag liner

If you don't like to wear your insulated clothing in your sleeping bag like many people, then a VBL liner makes more sense

You can't beat months of real-world testing. If the quilt, top and bottom, was made of cuben I suppose the insulation was kept fairly dry so condensation wasn't a problem?

I agree! Both the top and bottom of the quilt are cuben, and so are the baffles. There is one vertical stripe of M90 fabric on the outside of the quilt that runs perpendicular to the cuben baffles (horizontal baffles, vertical stripe). This is similar to Tim's original quilts, before he stopped using the stripe. I did keep the quilt very dry. It did become wet with condensation on the outside as my bivy created condensation from my breath, but I had no problem getting rid of that with a few minutes in the sun.

I have a Tim Marshall quilt that is all Cuben inside and outside fabric. It doesn't work as a VBL, because I can vent it as the need arises. But with this system you really need to plan on it working down to the lowest temperature you expect – no wearing insulation under it, especially down. I have a VBL sleeping bag liner for use inside a sleeping bag, but the temp needs to go below 20F for it to work properly for me.

"It sounds to me like rusty b already has a fair amount of experience using a vapor barrier and he finds that it works for him. Responses so far seem to be missing the point of the original post".

Thank you, Colin! ….and Evan.

"My VBLs are usually plastic bags so I toss them away at the end of a trip."

What kind of plastic bag do you use?

I've been playing around with the idea of using a VBL to solve the condensation problem bivies inevitably have under certain conditions. I've just been taping trash bags together, but it seems like there must be a better way.

"What kind of plastic bag do you use?"

When used on my feet only, I use the bags you put bulk food in at the grocer. They get pretty ripe smelling after a single night.

Around mid summer, I got a 72" long garment bag from the local dry-cleaner for $.25 cents. Only used it a few nights. Rather than toss this one, I rinsed and kept it. It weighs 1.56 oz. Simple, cheap, readily available, light and effective. I like it quite a bit.

You probably already know all this but…while a VBL will keep your body moisture out of your sleeping bag, it may not prevent condensation on your bivy. When your body heat escapes through the bag and makes contact with the cold bivy material, it still could be prone to condensing. Only way to know for certain though, for your particular conditions, is to try.

"Around mid summer, I got a 72" long garment bag from the local dry-cleaner for $.25 cents."

Brilliant, thanks. Exactly what I was looking for!

"while a VBL will keep your body moisture out of your sleeping bag, it may not prevent condensation on your bivy. When your body heat escapes through the bag and makes contact with the cold bivy material, it still could be prone to condensing."

I need to read up more on the science behind this and do more backyard testing. However, with the VBL in place you aren't introducing more moisture into the system – just heat. This means you only risk condensing what water vapor is already there.

I thought condensation formed because warm air can hold more moisture. As air cools, it loses its ability to hold as much water vapor, and some of the excess vapor turns into liquid water / condensation.

I think simply heating up and cooling down air shouldn't cause condensation if the moisture content of the air stays constant. I dunno, though.

I think you;re right Pete – no condensation if you have an effective VBL

maybe water vapor leaks around the edges or through holes or whereever

It may be different in the context we're talking about here. However, in architectural training, I was always taught condensation in a building typically occurred when warm air came into contact with a cold surface. An example in buildings would be the roof sheathing. Warm air that escaped through the ceiling and insulation would hit the cold underside of the roof and condense. The moisture drips on to insulation and also rots the sheathing. The plastic vapor barriers under the sheet rock do not prevent this …at least not in all environments. I've seen first hand the damage this can cause to a building's internals. In the context we're discussing here, the cold surface would be the bivy. Easy to design a roof to eliminate this issue. Maybe not so easy in a bivy.

Putting the vapor barrier between the house and insulation doesn't work? So like, ceiling -> vapor barrier -> insulation -> roof.

I think maybe a good analogy might be the air inside a car in winter. Turn on the heat and sit in your car for a while, then get out, close the doors/windows and let it sit outside in sub-freezing temps. As the air inside cools, moisture that your body and breath introduced to the car will condense and you end up with frost on the inside of the windows.

Next, "reset" it by letting your car air out. Close the windows and let it sit in sub-freezing temps. Now there is no frost on the inside of the windows and the air inside the car is as cold as the air outside.

Go out, turn the car on, blast the heat, but don't sit inside it. After a while, turn the car off and wait for the air to cool down again. Theoretically, there should be no frost on the windows because you didn't introduce more moisture into the system – all you did was heat and cool the air.

I could be wrong about this, I have no idea, I'm just speculating. I'm pretty sure there's a big BPL article somewhere about the science behind condensation but I've been too lazy to read it thus far.

"Putting the vapor barrier between the house and insulation doesn't work?"

Yes, it keeps moisture created from cooking, bathing, breathing, etc from entering the insulation….just as a VBL keeps body perspiration out of the bag's insulation. However, it doesn't prevent heat loss that rises to the underside of the roof where the dew point is reached forming water. Proper roof ventilation prevents issues…and it removes heat build-up in the summer.

Another analogy, sorta, is setting a glass of ice water out in the summer. Water condenses on the outside of the glass.

I'm no scientist. Just passing along what I was always taught and have seen in the building field. :)

"Another analogy, sorta, is setting a glass of ice water out in the summer. Water condenses on the outside of the glass."

This happens because that warm summer air has a lot of moisture in it and then it gets cooled down to the point where it can't retain that moisture.

The difference here is that in your example, we are taking air that WAS warm and cooling it down. In the bivy example, we are starting off with cold air, warming it up, and then cooling it down again. Unless we add moisture or we cool it down to a lower temperature than it started at, we shouldn't get condensation. Theoretically.

Maybe we will have to agree to disagree until someone who IS a scientist comes and straightens this out :-p

I didn't realize we were disagreeing. :-)

In the building design fields, I believe the exact science here is only partially understood by most. However, at the same time, enough is known by the majority to minimize or eliminate moisture problems in roofs (primarily during winter months) through the mechanisms I mentioned prior….at least in my locale.

I kind of expect that roof condensation is more of a pain to deal with because a building is a big and complicated thing. Even if you manage to get a 100% no leaks vapor barrier between the house and insulation, some moisture can still come in from other places.

It's probably much safer and easier to take as many precautions as you can so that if/when some moisture does find its way in there somehow (from below, from above, from the sides, etc), you minimize the potential for condensation.