Mesh vs Vapor Barriers for sleep systems

[Joe M]

With the latest editorials focusing a lot on mesh fabrics for base layering during winter, I’m curious how they compare with vapor barriers as part of one’s sleep system. Mesh doesn’t really address the potential for excess moisture migrating into down bags during extended winter trips. I’ve seen several examples of using a light (50°) synthetic top quilt over the main down bag to mitigate this issue, but which provides the best warmth to weight ration and performs better?

[Bill Budney]

Hmmm… define “performs better”?

Mesh and VBLs are unrelated. VBLs are specific things for specific purposes. If you have never used a VBL then you should try one before investing a lot of money. Climb into a large trash/contractor bag and try to sleep. You’ll get the idea soon enough. Yes, a VBL protects your bag from sweat, but the cost (in comfort) is pretty high.

The synthetic layer over a down bag can move the condensation to the synthetic layer, which can handle moisture a little better. This happens without compromising your comfort, which is why you see it often recommended.

If you have time and sunshine in the morning, then you can dry your bag in the sun before packing up. This is why many down bags have a dark side, which warms quickly in the sun. No synthetic layer required. (In polar regions during Winter, you may have no choice but to use a VBL).

VBLs tend to be more commonly used for hands and feet, both of which can be difficult to keep warm, but can tolerate some moisture. Boots can be especially difficult to keep dry in sub-freezing weather, so VBLs (or WPB socks) are common ways to help. They may not keep your feet 100% dry, but they will prevent sweat from adding moisture inside your boots, and will prevent outside moisture from reaching your feet. I like the balance and comfort of SealSkinz, but others have been happy with just a plastic bag, while still others prefer GoreTex.

For strictly warmth to weight, VBLs weigh almost nothing, so they win. But whether or not you will like them for a specific job requires trying them. For emergency use, a couple of pairs of nyplex (or food-handling) gloves and a couple of plastic bags for your feet are cheap and lightweight insurance.

For high warmth to weight AND excellent moisture management, then alpha direct is hard to beat. Mesh is a variant that leans toward the moisture management side. Many love it. Gram for gram, I would more often choose AD. When I don’t care about the weight, I wear both.

 

[Mark Verber]

I pretty much agree with everything Bill said, though didn’t find VBLs as uncomfortable for sleep. When the outside temp were <=10F, my bag wasn’t over insulated, and either was made from a fuzzy knit, or wearing an ultralight synthetic base.

As Bill noted, VBL for gloves and shoes work really well in cold conditions even when active.

[Joe M]

By performs better I’m referring to comfort while sleeping and adding to the insulation effect of your quilts.

Yes, I’ve tried some makeshift VBLs and discovered pros and cons. They definitely help with the warming effect, and I never experienced any of the claiminess others mention. But I did notice the VBL can’t be overly loose or it will still lead to some skin cooling.

My main question is I’m curious how mesh and base layers will perform in sleep systems, especially over multiple days.

[Bill Budney]

All will work.

Alpha Direct will be warmest per weight. Mesh would be nicer in warmer weather. Other base layers in between.

[Bill Budney]

Another way to look at this is that most base layers are roughly similar. Cheap polyester performs 80% as well as the most exotic tech fabrics. So we are discussing fine points, rather than huge variations between different kinds of fabrics.

If you have not tried alpha direct, then it is the most different, so it is a great choice for your first experiment. It’s still fleece, but it is lighter and has large holes that move moisture similarly to mesh. Put a wind layer over it for high warmth, or leave it uncovered for excellent air permeability and cooling. It is versatile. Can be used as a base or mid layer, and looks acceptable in public. Will add warmth to your sleeping bag.

Mountain Hardwear’s Airmesh (Teijin Octa fabric) has many of the benefits of alpha direct and looks nicer, if that matters.

Mesh is more single-purpose, but it works well for moving moisture off of your skin. It is nice under a rain jacket. However, it is clearly underwear; not something that most people would wear, uncovered, in public.

Broadly speaking, I would call AD, “insulation” while I would call mesh, “moisture mangement”. Yes, mesh adds some insulation as well, but not as much as AD.

[Joe M]

By your comments, I’m goings to assume you haven’t listened to Ryan’s latest podcast discussing mesh.

[Bill Budney]

LOL.

Just reporting a different POV. Or perhaps adding more detail. It is not even an entirely different experience. Ryan points out the similarity between AD and mesh around 41 minutes in.

[Moab Randy]

I have sewn silnylon vapor barrier liners into both of my Western Mountaineering down bags and used them for decades. The liners are contoured to mimic the bags’ interiors and are sewn to the zipper and tied to a few points on the inner bag seam so I can replace them every few years when they get too dirty.

I don’t do snow camping, so I can’t report on their efficacy for that, but I use these for all of my backpacking, desert or mountain, and wouldn’t do without. They do stop most of the vapor migration into the down, keep the bag interior pristine, and, most importantly to me, they add a great deal of warmth and wind resistance.

The experience is nothing at all like the mentioned “trash compactor bag” result. The problem with those bags is that you get all wrapped up and twisted like a fish and they have no way to ventilate. I use my bags essentially like quilts most of the time so I have all the ventilation I need to keep the bag from getting too clammy. When it gets cold I zip up and then I’m very happy to have the extra vapor because water holds so much more heat than dry air.

Does it feel clammy or soggy? Most of the time, not, just cozy. When I zip up, there are certain crossover temperature/wind/humidity conditions where it sometimes does feel clammy, but on average I’ll take those instances over going without. I usually sleep naked, so maybe the answer is just to put on some of that underwear, mesh or not.

My main complaint is that my feet often get clammy because there is no ventilation at the end of the bag to use for the not-so-cold conditions. I would say that anyone who uses a quilt with foot ventilation would be missing a great opportunity if they don’t line their quilt with a VB. It could even allow you to use a lighter quilt for an equivalent warmth.

[Dave @ Oware]

When VBLS became into vogue in the 70’s (not counting Bunny Boots in Korea) it was just before Goretex and the recommendations were to wear a fishnet shirt under a coated nylon parka with long pit zips for venting or even wearing like a vest with arms out. Then Goretex hype kinda doomed VBL’s except for long winter trips. Being able to cool and vent is key, so mesh underneath makes sense and is more comfortable I think.

[Paul McLaughlin]

VBL’s require management to be comfortable and effective in a sleep system. You need to maintain a very narrow range of temperature in which you are warm but only just, so that you are only generating “insensible” perspiration (which is what your body does always in order to keep your skin from drying out), and not “sensible” perspiration, usually referred to as sweat, which is generated to cool the body. The temptation when you begin to sweat is to vent the vbl, when instead you should reduce the amount of insulation. If you vent the vbl you start a vicious cyle, sweating and then venting the vbl, ending up losing more heat than you would without the vbl. Precisely why I have never tried it, because my body’s heat output seems to vary widely during the night and trying to manage the insulation to suit seems like it would keep me awake half the night. But if i was to try it I would go with a vbl suit rather than liner; that way if you get up to take a leak you take the vbl with you, plus you have the option of wearing clothes over it if you need the extra warmth.

As for mesh vs. Vbl I don’t think an either/or makes much sense, they are so different- plus they could go well together, as it is usual to wear a synthetic baselayer inside a vbl and that could be mesh.

As for AD, that I have tried and I love it, have made two pairs of pants , the lightest is half the weight of any base layer I have ever had and about as warm as conventional expedition weight stuff when worn under something or in the bag. And very comfy to sleep in.

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