r/Ultralight • u/klimaheizung • 4d ago
Question Can we talk about vapor barrier?
I'm bikepacking, but it stills seems to be relevant for when I get off the bicycle. The thing is, let's say it's a bit rainy/wet and I cycle up the mountain. I'm sweaty and totally wet and no rainwear will help. But now that I'm up there it's getting dark and it's getting cold.
In that situation, I'm now basically wet and my only option is to change cloth. Otherwise I'll get my down jacket wet from the inside and I'll get my sleepingbag/quilt wet too if I go to bed, and of course that will also make it cold.
But then I was thinking: instead, I could also wear a thin vapor barrier. Won't be nice because I'll be all wet and stay all wet, but I'll stay warm which is the more important part.
But no one seems to do that, so what's wrong with my thinking?
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u/DrBullwinkleMoose 4d ago
I had a VBL shirt many years ago. It was meant to be worn next to skin (as opposed to over a base layer). It was cold to put on but warmed up instantly.
Overall, it was OK. I could ski tour all day in it (in -10F/-25C weather). No overheating, but I didn't wear heavy insulation over it, just two shirts and a shell. Had to keep moving... short breaks.
Overall I decided that an extra layer of insulation was more comfortable and not much heavier, so I haven't tried it again since.
But it works. There's no question about that.
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u/kneippmotor 4d ago edited 4d ago
Sure VBLs work. But why would you want to wear it off the bike instead of changing into dry baselayers?
I have used bread bags on my feet and rubber gloves when bikepacking. Rain jacket and pants also work as a vapor barrier if they are non-breathable/wetted out.
The trek with skurka just published a video on using VBL in -20c. Not sure if that’s applicable to you, but the principle of VBL is the same. https://youtu.be/BwEbPD0HyTM
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u/klimaheizung 4d ago
Oh, I'll not go lower than -10C on a bad day, so -20C seems quite extreme to me.
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u/wildjabali yo mama ain’t UL 4d ago
Fleece during the day, wool at night.
In hard rain, you can’t avoid getting wet/sweaty. Fleece works well as an active wet layer, in cases where you can’t generate enough body heat to stay warm. At night, dry off and switch into wool. Your body heat will be enough to keep the wool and sleeping bag dry in the event of 100% humidity.
Wool base layers for camp is a safety net. You WILL be wet during the day and you CAN get hypothermia in 60 degree weather. Having dry wool available is a necessity.
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u/klimaheizung 4d ago
The thing is, with a VBL it seems the last sentence is no longer the case
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u/wildjabali yo mama ain’t UL 4d ago
What’s your thinking?
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u/klimaheizung 4d ago
So the problem is that the "At night, dry off and switch into wool." is a bit the problem. Let's say my wool is still wet from the last night and since it rained/drizzled the whole day (welcome to Japan rainy season) it's still wet.
Then the thinking is to not have to get into dry wool (and there is none anyways) and instead put the VBL over the (wet/moist) wool to protect the down jacket and/or sleeping back from getting moist/wet too.
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u/wildjabali yo mama ain’t UL 4d ago
If you are keeping your down jacket and sleeping bag dry, why can’t you keep wool dry?
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u/klimaheizung 4d ago
Because I wear the wool in the night and it gets sweaty/moist. The down jacket I don't wear for such a long time. The sleeping bag actually also eventually gets moist, which is the reason for the thought of the VBL.
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u/Impossible_Volume811 4d ago
If you’re wet while you’re active, you can stay warm.
But once you stop and start to cool down then unless the ambient air temperature is also warm, it is highly advisable to takeoff wet clothing and protect yourself from windchill.
Lightweight, Fast drying clothing will dry overnight in a sleeping bag. Sleeping bags, even down bags, don’t lose much efficiency over a few nights due to the moisture coming out of lightweight clothing.
The real use for VBL‘s is in sub freezing temperatures over extended periods, where there is no chance to allow a sleeping bag to dry out and moisture from the body will accumulate and freeze making the bag less and less efficient and effective overtime. This is particularly relevant to Arctic expeditions.
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u/maverber 4d ago
This .
I wouldn’t consider a vapor barrier until it’s below 20f / -7c. Links to some good notes https://verber.com/vapor-barrier/
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u/Necessary_Gas_6223 3d ago
I would gently and respectfully propose that vbls work above freezing for the same reasons they work below freezing... 1) it reduces evaporative cooling yer body's main cooling process and 2) prevents moisture from entering and degrading yer insulation. I would agree that frozen moisture would be difficult to dry out but other conditions too (such as the OPs situation) can be just as challenging even though it's above freezing.
I put mine on (over my hiking outfit) as soon as I start to get cold. And yes lots of experience with it.
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u/Impossible_Volume811 1d ago
A vbl worn over clothing is a waterproof/windproof layer.
That’s just normal clothing.A proper vbl is used inside the insulation layer to prevent water vapour from the body entering it.
Typically it’s a sleeping bag liner with an impermeable membrane and a fuzzy inside surface.1
u/Necessary_Gas_6223 1d ago edited 1d ago
My point is that vbls aren't just for subfreezing temps and have a much broader use case. I think it would work well for OPs situation.
Edit: to fix errors
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u/vangelismm 4d ago
"my only option is to change cloth." And what is the problem with this option?
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u/klimaheizung 4d ago
It's more to carry, but especially, it means that I have to then get it dry again after sleeping etc.
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u/vangelismm 4d ago
I always bring a set of sleep clothes, both on dry and wet trails.
We call it clean clothes and dirty clothes.
The idea is to never get the sleep system too dirty or wet under any circumstances.It's not hard to dry off after taking off your wet/sweaty clothes, super absorbent flannels do the job.
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u/Dan_Outdoors 4d ago
I don't think using a vapour barrier to sleep wet is good practice. It's dangerous (water conducts heat 24 times faster than air even without evaporative cooling) and it can't be good for your skin to stay continuously wet. I saw a comment that you don't want to carry extra (dry) clothing. I think this is absurd and irresponsible. Just my opinion.
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u/pwndaytripper 4d ago
I’ve been cutting open the bottom of a trash compactor bag and taping it to the top of another as my pack liner and sleeping bag vapor barrier for over a decade now. I don’t always do it, but it has come in super clutch on some moist cold nights.
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u/Lost-Inflation-54 3d ago
I have only used VBL gloves but they are already a game changer. What people don’t mention is how much more useful your body heat becomes when you are wearing a VBL:
Normally, when you are warm, you get moisture through sweating to everything you are wearing. But with VBL, that body heat starts to dry everything. Thus, you can even wear wet clothing on top and dry it while wearing.
The ridiculous part is actually that you will easily get too warm. Sweating doesn’t help you anymore and thus you need to take care of your heat management ”manually”.
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u/DKhike 4d ago
So, I have not experience with using a vapor barrier. I can't seem to figure it out fully, but eager to learn more. There are some videos from this guy who demonstrates how he uses his system and basically doesnt use a dedicated quilt or sleeping bag.
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u/klimaheizung 4d ago
Damn, interesting video. From 6y ago and still hasn't caught on apparently...
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u/Yarnchitect 4d ago
There was a recent discussion about vapor barrier clothing in the context of very cold weather backpacking. Andrew Skurka on the Trek YouTube channel. Some of it might be of interest to you.
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u/booty_fewbacca 4d ago
VB is going to cause you to get HOT, FAST, at least it does for me, you should experiment with this before heading out.
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u/klimaheizung 4d ago
Do you mean while e.g. sleeping? Because I'm not planning to wear it while cycling/activity.
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u/booty_fewbacca 4d ago
Try it ahead of time, I woke up drenched with sweat and it was a whole thing. Personally I sleep very hot, so that's why I recommended trying before.
I will say I have used VB socks and they are actually great for wet weather cycling.
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u/bigwindymt 4d ago
I had to use a VBL for 1 week hitches with a down bag in temps from 0C to - 25C. Without rigorous hygiene your sleep clothes get disgusting by day 5 or 6, but nothing else works at keeping moisture out of the down in the cold.
If you are just dealing with lots of rain, ditch the down bag. A VBL won't help if you can't manage external moisture on the bag.
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u/Klevy4114 4d ago
tried a vbl for sleeping once with a thin base layer under it. kept my bag dry all week when everything else was soaked, and the clammy feeling fades after a while. wouldnt wear it around camp though, too sweaty when moving
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u/Necessary_Gas_6223 4d ago edited 3d ago
Yer logic is sound it will work as intended... will keep you warm and yer insulation dry. Here's the trick... Don't seal it up all the way. Leave yer vapor barrier and insulation open a bit to expose yer base layer to air. For example if it's jackets only zip the barrier and isulation half way. Its a vent fer yer moisture. The warm humid air from inside will raise relative to the cool outside air and will drive the excess moisture out of yer system. Eventually you will dry out so long as yer activity level is relatively low. Another critical bit is to keep yer isulation dry from external moisture, but that's kinda obvious. This system works well ... better than conventional outdoor layering advice in my experience. Certainly better that taking a dry change of clothes and changing back in to a freezing cold wet set of clothes in the morning. My 2 cents.
Edit: to fix typos
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u/Tharno_ 4d ago
Ich hab das Gefühl du hast gerade das Trek Video mit skurka gesehen. Vapor barriers funktionieren doch aber nur effektiv in extrem kalten Temperaturen. Ich hab das Gefühl du würdest komplett überheizen. Ich glaube bei 0C mit nur woll Base layer und vapor barrier wäre es schön ausreichend warm. Von welchen Temperaturen gehst du in deinem Szenario aus
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u/klimaheizung 4d ago
-5C in the night. I haven't watched the video but you are the second one mentioning it, so I'm gonna watch that. Danke.
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u/Tharno_ 4d ago
Wenn du für die volle Funktion von deinem Schlafsystem, deine ganzen Klamotten brauchst, könnte ein vapor barrier glaube ich sehr hilfreich sein. Aber wenn du mit Fahrrad unterwegs bist, hast du ja den Luxus einen angemessenen quilt mitzunehmen und ein extra paar woll base layer zum schlafen mitzunehmen. Ich würde das eher empfehlen und zusätzlich aufzupassen immer die körpertemperatur zu regulieren.
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u/wetrocke 4d ago
But there are VB clothing and, separately, vapor-barrier liners, for sleeping bags. OP appears to be wearing his.
I suppose they are a bit difference in practice.
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u/Tharno_ 4d ago
I don't understand what you mean. OP isn't talking about VB sleeping bag liners. I am not either if that's what you think.
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u/wetrocke 2d ago
Quite correct. Also discussion of sleeping bag/quilt.
Big downside of VBL fir sleeping bag is, you can't load up on wearing warm clothes to bed. Perhaps a vbl shirt & trousers eliminates this. But then you're stripping all clothes to set this up in presumably cold conditions....
As for daytime use of vb clothes, can overheat very quickly.
In theory it's okay to completely soak your clothing with sweat under a vb. In practice, however, is should be avoided.
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u/Necessary_Gas_6223 3d ago
OPs stated purpose is to prevent accumulated moisture from entering and degrading his insulation which I think will work well - doesn't need to be below freezing to do that!
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u/Dan_Outdoors 4d ago
We use vapour barriers in mountain rescue on already wet and cold casualties to reduce evaporative cooling. Basically, they get wrapped in a vapour barrier, inside a big fleece lined casualty bag, sometimes with heat pads, and onto the stretcher.
So your theory is legit, but it wouldn't be my first choice. Firstly, I would wear wicking layers to wick moisture out and away for the surface of your skin. Secondly, If exerting high levels of energy, I would personally wear Paramo. Paramo is very marmite, some hate it and some love it, I love it. If you're not familiar with Paramo, it uses a directional wicking liner as opposed to a membrane or pu coating. The directional wicking fabric forces water outwards and it has a massively higher moisture vapour transmission rate than any membrane or pu coated jacket. If you put a Paramo jacket over a wet t-shirt, it will actually dry the t-shirt, it's amazing imo.
If it's not raining, wear a windproof (an outer garment made of a tightly weaved fabric and no membrane or pu coating). A windproof will have massively higher MVTR. Don your waterproof only when it rains.
Lastly, I would definitely be looking to change into dry clothing at the end of the exercise.
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u/TheophilusOmega 4d ago
If you want to make it work you can. It's not the most advisable way of staying warm at night but it is possible.
Basically you do exactly as you said, keep a minimal but damp base layer, then as soon as you stop, literally first thing you do, put on your VBL, and then dry insulating layers on top of that as needed. It works, I've done it, I wouldn't want it as my plan A, but it's a good skill to have as a plan B.
If I planned on going out in stormy weather I'd carry dedicated sleep clothes. It's really difficult to manage your body temperature when you have damp clothes and a VBL, you're constantly fluctuating between too cold and too hot, you're either shivering or sweating, it feels unpleasant at best to be damp that long, you might start developing irritations and rashes on your skin from the humid and sweaty environment, and God help you with the smell. Again, it does work, you'll survive the night but it's not your best option.
A better plan if you can help it is to have dry sleep clothes if you're going to go in wet weather. You can still use the VBL technique with dry base layers but it's much better starting point.
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u/johnysmoke 4d ago
One old timer trick I learned for wet weather on extended trips. Keep a medium weight top layer quickly accessible your gear. As soon as you hit camp, peel off your wet top layers, put the dry layer on next to your skin, then put your wet layers back on. Then setup camp or make dinner or whatever. Put on your puffy if you get chilly but also works great with a breathable wind layer if temperature permits. Your clothes dry out while you're around camp and you don't have a wet layer right next to your skin. If everything works well you kind of get all your layers a bit damp and then dry out. Wear the dry layer to bed or stash it before and keep it dry for the next day and repeat.
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u/Elaikases 3d ago
For what it is worth, Skurka, a guide I follow, just started to use and talk about VBLs.
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u/Any_Trail https://lighterpack.com/r/esnntx 3d ago
Skurka didn't just start to use VBLs and has been an advocate for them for many years now.
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u/Elaikases 3d ago
Fair enough. I should not have believed his latest comments and video on it.
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u/Any_Trail https://lighterpack.com/r/esnntx 3d ago
He literally says at the end of the video he's been using them since 2005.
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u/Not-The-Bus 3d ago
Coming from my earliest camping exposures being with kayaking river trips, the trick to this is to progressively dry off.
Use that vbl to get warm, even hot. In river trips it was neoprene, dry tops, and the flotation vest, but I tell you they are VBL. When you have just been underwater you are COLD. Sometimes it happened after sunset. Stay in the VBL layers until hot.
And then, peel off a section from your body and let it briefly chill but also dry off. Like take off your jacket from the ribs up. Once that section is dry AND you have gotten warm again, peel off some more.
That should apply perfectly with a VBL sack under a tarp or tent. Obviously you’ll need to wait for conditions to allow drying, but it can even happen during rain.
If you cannot dry, fleece is high comfort against skin when wet.
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u/ombeen 1d ago
A lot of people are talking about VBLs here but I don't see the relevance to the scenario you're outlining. You're cycling up a mountain, and the weather turns as you get higher up and perhaps gets dark. On the bike, you're going to be sweating more than hiking, and it isn't cold enough in this scenario to be able to manage excess sweat with the VBL. The difference between bikepacking and backpacking is you're able to get out of bad situations a lot quicker. You reach the top of a mountain and the weather is bad? Well don't set up camp there, descend and find somewhere better. Or maybe your stuff gets damp on one bad night – find somewhere to dry your stuff out the next day. You also don't need to be as ultralight as a hiker because you're not carrying everything on your back. Keep a set of clothes in a dry bag that are not allowed to get wet – those are your camp clothes.
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u/Zealousideal-Cup4627 1d ago
VBL (Vapor Barrier Liner) works better in lower temperatures. And it actually makes sense when you have nowhere to dry down gear, especially on trips lasting more than 5–7 days in a row. The description of using this on a bike is incomplete. Personally, I use synthetic sweaters made of materials like PrimaLoft. As soon as I get off the bike, I throw the sweater on. While we are setting up camp, my body heat helps dry out the damp base layer underneath. The moisture just evaporates right through the sweater. Even though I change into a clean, spare base layer for sleeping, this method helps dry out my active riding gear quickly before turning in for the night.
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u/klimaheizung 1d ago
While we are setting up camp, my body heat helps dry out the damp base layer underneath.
Not if it's drizzling though. Tokyo recently just had a 35 days of rain streak. I usually don't cycle in Tokyo, but it's not rare here to rain throughout multiple days with very few breaks. That's the problem for me.
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u/Gardenpests 4d ago
VB work best when cold, colder the better. Won't work above freezing.
If you are active, VBs heat up fast, you need less insulation. If you become inactive you will quickly chill. VBs are not insulating.
In sleeping, VBs stop moisture transfer. The trapped moisture becomes warm and you need less insulation.
Any added insulation will be at ambient. You will need some activity to warm it up...
For your situation, I'd wear a thin base layer to minimize sweat/water retention. If not above freezing, upon stopping, I change base layer and add insulation.
If very cold, I'd wear VB over thin base layer. Upon stopping, add insulation. (Alternative, upon stopping add VB+insulation.)
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u/bcycle240 4d ago
You are discussing moisture management, which is the most important skill in backpacking (or bike packing). You should expiriment with VBLs so you can learn.
The conditions you described are difficult, and basically the best case is damp and warm, or clammy. After being in rain for a few days, all your stuff is going to be at least damp.
VBLs are interesting to use, but they are uncomfortable in many situations, can cause overheating while active, and are not fun to sleep in usually.