for people wanting to go super ultralight look at this

**ikemouser** · 05-20-2010, 09:01

I strongly disagree as well. It may be cood for winter though, really cold winters.

**bigwig** · 05-20-2010, 10:40

Originally Posted by gargoyle

So, sleeping in a plastic bag is a good idea

I strongly disagree.

Next time you sleep in the winter, weigh your bag before you leave and then weigh your bag in the morning to see how much water your bag has absorbed and even had frozen inside. I've done it before and found my bag to be about 1 pound heavier in the morning (on a 2 pound 4 ounce bag). Some people have reported much more water in their bags than that. VBLs eliminate evaporative heat loss and the amount of sweat you retain in the VBL isn't really all that much as you sweat less in a VBL than you do when the sweat is quickly evaporating off your skin. I definately think that there's a place for VBLs, like in very cold temps. I've slept in my lightweight 3 season bag (30 degree rating) in temps down toward -20 while wearing my goretex coat and pants (not a true VBL but it still slows the amount of evaporative heat loss). I know several people that swear by their VBLs.

Just saying, I think there's a place for them and that some people have a lot of success with them.

**sclittlefield** · 05-20-2010, 12:05

Originally Posted by Mountainfitter

Non-breathable sleeping bags and quilts are actually better then breathable ones since your sweat will never wet out the down.

This is true. It just takes a LOT more know-how on temperature regulation than most campers and backpackers care to bother with. For most people, it's not ideal, but for the serious ultralighter who understands thoroughly how to use a vapor barrier (VB) effectively, the benefits won't be overlooked.

While I understand some of the theory here, due to the extra thinking/planning/paying attention to factor - I personally prefer not to employ the VB techniques. But they are very effective, and I may rethink it a bit this winter.

**drewboy** · 05-20-2010, 13:30

It's just wrong to make a generalized statement like that. Vapor barrier type arguments only apply to a specific set of conditions.

Originally Posted by Mountainfitter

Non-breathable sleeping bags and quilts are actually better then breathable ones since your sweat will never wet out the down.

**ikemouser** · 05-20-2010, 13:44

Originally Posted by bigwig

Next time you sleep in the winter, weigh your bag before you leave and then weigh your bag in the morning to see how much water your bag has absorbed and even had frozen inside. I've done it before and found my bag to be about 1 pound heavier in the morning (on a 2 pound 4 ounce bag). Some people have reported much more water in their bags than that. VBLs eliminate evaporative heat loss and the amount of sweat you retain in the VBL isn't really all that much as you sweat less in a VBL than you do when the sweat is quickly evaporating off your skin. I definately think that there's a place for VBLs, like in very cold temps. I've slept in my lightweight 3 season bag (30 degree rating) in temps down toward -20 while wearing my goretex coat and pants (not a true VBL but it still slows the amount of evaporative heat loss). I know several people that swear by their VBLs.

Just saying, I think there's a place for them and that some people have a lot of success with them.

You sweat 16oz a night? that must be a record. mine weigh about the same. I think part of your problem is your sleeping in goretex

**bigwig** · 05-20-2010, 14:48

Originally Posted by ikemouser

You sweat 15oz a night? that must be a record. mine weigh about the same. I think part of your problem is your sleeping in goretex

Wow. This is the first semi-rude post I've seen on these forums; usually they are so pleasant. Anyway, not all the moisture is from sweat, but the average person sweats about 1-1.5 liters of water a day. A liter weighs 1 kilogram. If, as most people, you sweat more at night than in the day (at rest) and you've spent about 8 hours in your bag, almost a pound isn't unreasonable. Even more moisture is lost through breathing and the water saturation around your face can add quite a lot to it. I'm a big guy and I do sweat a lot.

The only way that your bag weighs the same in the morning as when you go to sleep, if you're not using a VBL, is if your body heat is keeping the water molecules heated enough that they are pushed all the way through the insulation on your bag before it freezes (some evaporation can occur directly from ice, but not much). If that is happening, as you say, to 100% of the water that you've sweated, either the air is incredibly dry around you, or your sleeping bag is doing an absolutely horrible job of insulating. Either way, you would have a ton of evaporative heat loss; you'd be cold. So, either you have only weighed your bag when it was warm and dry that night, you need a new scale, or you haven't actually weighed. You may be the only person that doesn't have to worry about airing out your bag in the morning or when you get home.

I think part of your problem is your sleeping in goretex

Really, this shows that you don't know much about how VBLs work. A higher humidity next to your skin slows down sweating; it doesn't speed it up. Plus, with wpb gear the rate that the moisture comes off the wpb material would be slowed, resulting in less sweat in your bag. Wpb gear isn't a true VBL but, in my exerience, it still helps. I do wear true vbl socks (your feet are one of the major sweat producers in your body).

Anyway, you most certainly don't have to use it, and since the humidity around your skin is more humid with it some people find it uncomfortable. There's just no doubt, though, that it will keep you warmer, especially in very cold temperatures. I don't feel strongly about it one way or the other, as opposed to your "I strongly disagree." I was just trying to point out that there are most certainly benefits to it.

**ikemouser** · 05-20-2010, 15:03

Originally Posted by bigwig

Wow. This is the first semi-rude post I've seen on these forums; usually they are so pleasant. Anyway, not all the moisture is from sweat, but the average person sweats about 1-1.5 liters of water a day. A liter weighs 1 kilogram. If, as most people, you sweat more at night than in the day (at rest) and you've spent about 8 hours in your bag, almost a pound isn't unreasonable. Even more moisture is lost through breathing and the water saturation around your face can add quite a lot to it. I'm a big guy and I do sweat a lot.

The only way that your bag weighs the same in the morning as when you go to sleep, if you're not using a VBL, is if your body heat is keeping the water molecules heated enough that they are pushed all the way through the insulation on your bag before it freezes (some evaporation can occur directly from ice, but not much). If that is happening, as you say, to 100% of the water that you've sweated, either the air is incredibly dry around you, or your sleeping bag is doing an absolutely horrible job of insulating. Either way, you would have a ton of evaporative heat loss; you'd be cold. So, either you have only weighed your bag when it was warm and dry that night, you need a new scale, or you haven't actually weighed. You may be the only person that doesn't have to worry about airing out your bag in the morning or when you get home.

Really, this shows that you don't know much about how VBLs work. A higher humidity next to your skin slows down sweating; it doesn't speed it up. Plus, with wpb gear the rate that the moisture comes off the wpb material would be slowed, resulting in less sweat in your bag. Wpb gear isn't a true VBL but, in my exerience, it still helps. I do wear true vbl socks (your feet are one of the major sweat producers in your body).

Anyway, you most certainly don't have to use it, and since the humidity around your skin is more humid with it some people find it uncomfortable. There's just no doubt, though, that it will keep you warmer, especially in very cold temperatures. I don't feel strongly about it one way or the other, as opposed to your "I strongly disagree." I was just trying to point out that there are most certainly benefits to it.

Didn't mean to be rude, just seemed unreal for a quilt to gain that much weight overnight thats all. not meant to be personal at all, if i knew you would be sensitive about it, of course i would have left it out. My apologies, it was a gut reaction. I don't sweat that much so maybe thats why it seemed strange. I also use vbl socks in winter, and a vbl top in winter, but not to sleep in. I do sleep in the socks but not the top.

**NCPatrick** · 05-20-2010, 15:04

Yep, Youngblood had some really good posts describing how vapor barriers work. I've experimented with it some as well. It (the theory) works really well in practice at or below certain temperatures. Obviously once the temp rises you would not use a vapor barrier.

**Quoddy** · 05-20-2010, 15:37

I talked with Steve a lot while this quilt project was underway. We both knew that there would be a downside or two making it in cuben, but the idea was to make it as minimal/lightweight as possible. At the same time, I was having a quilt made using 0.8oz Quantum. Although my quilt is fractionally heavier, I think it's a bit more practical in most situations.

**Quoddy** · 05-20-2010, 15:38

I talked with Steve a few times while this quilt project was underway. We both knew that there would be a downside or two making it in cuben, but the idea was to make it as minimal/lightweight as possible. At the same time, I was having a quilt made by Nunatak using 0.8oz Quantum. Although my quilt is fractionally heavier, I think it's a bit more practical in most situations.