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  MUSA Vapor Barrier Liner

Maybe more in Fall 2015
Made in: the SF Bay Area

product code: CAMP14

Made in USA Vapor Barrier Liner. Designed and produced right here in the Bay Area.

VBL, WTHeck?

This is a long explanation about a topic not many people understand, but one that's useful to know if you sleep outside often. It takes about ten whole minutes to read, and I don't recommend it.

A VBL is a liner for INSIDE your sleeping bag, to help you stay warmer, and to keep your bag and tent drier. But mostly the warmer part.

Vapor Barrier Liners have existed since the late '60s or so, and have flown well under the radar the entire time. They're a hard sell, because they're so easily and readily and instantly misunderstood nearly universally. But once you understand what they do and how they work and see for yourself, you be in the In-Crowd for perpetuity.

You lose heat four ways:

Conduction: Something cold touching you. That can be steel or air or water, but touching is key.
Radiation: Your body gives off heat like anything hot does. A mirror or a sheet of aluminum or a cloud cover reduces heat loss through radiation, which is why survival blankets are often aluminumized.
Convection: That's wind blowing away the thin, still layer of air that naturally resides on your skin.
Evaporation: Desert water bags and canteens work this way. You fill them with water, soak the fabric, and as the water evaporates from the wet fabric, the water inside stays cool.

Preventing heat loss thru conduction. When you're sleeping outside, the insulation prevents conductive heat loss. The thicker it is, the lower the temperature rating of the sleeping bag.

Preventing heat loss thru convection.The bag's fabric, and a tent do it--and that's assuming it's windy outside in the first place, which it may not be. But if it is, densely woven fabric blocks the wind and prevents you from getting cold via convection.

Preventing heat loss thru radiation. Well, it's not like you have to eliminate all forms of heat loss entirely. You take care of the conduction and convection, and you're off to a good start. If you want to block radiative heat on a clear night, sleep in a light-colored tent and/or wear something silver. Clouds reflect heat back down, which is why clear nights are colder than cloudy ones.

Preventing heat loss thru evaporation. This is a big one, just behind conduction in importance. You lose a pound or more of water per night through evaporation. That's a lot of heat loss. It's like sweating through your bag.

Your bag retains some of it, and on extended trips, can take on an extra pound of weight in your own sweat. Synthetics can handle this better than down can, but basically, dank insulation doesn't insulate as well as dry insulation.

And where does the moisture that passes through your bag go? Man, thanks for asking. It hits your tent wall, or your bivy sac. In cold weather, the fabric is cold enough to cause it to condense as frost immediately. You wake up with frost outside and on the side of your tent, and it's all because you didn't use a VBL.

People are afraid of non-breatheable fabrics because they associate them with sweatsuits. No, man, you don't understand.

It works like this:
Your body gives off moisture for two reasons only.

One is to prevent your skin from drying like old leather. To maintain a proper moisture balance, so your skin is young and dewy always. That kind of perspiration is called insensible perspiration, because you can't sense it. You can't see it on your skin because it's not wet sweat; and it doesn't feel like anything.

The other reason is to cool off. Dogs pant, people perspire. It was an adaption to leaving the shady forest and living on the hot plains of Africa 5 million years ago. (Apologies to creationists.)

So when you're too hot, you sweat, and the sweat evaporates.....ideally. Plastic suits make you sweat because they stop evaporation, so you get even hotter. Plastic suits are vapor barriers, but there's a big diff between jogging in a plastic suit on a hot day, and lying still at night in your sleeping bag.

You won't sweat or overheat in a VBL unless you have way too much insulation. A winter bag in the summer, for instance. Or even a winter bag in a snow cave (which is always 32-degrees or so) in the Winter. I used to do that, and I'd boil up. I'd have to get up in the middle of the night, get out of the bag and out of the VBL, and in the cool air the steam would come off me like soup. It was incredibly refreshing, and the point is: Use a bag that you'd be chilly in without a VBL. With a VBL to supplement it, your summer bag will work for you in the spring and fall, too. When you use a superlight bag in temperatures too low for it, the VBL easily makes up the difference, and you sleep warm and dry.

You have to know how to use them. It's not hard, but you can't do the wrong things. I've used VBLs for more than 98% of my outside sleeping since the early '70s, and I'll tell you how.

Here's how:
Dress in a light layer of wool, head to toe, so you're cozy. Any clothing between you and the VBL will interfere with your skin's ability to sense its moisture level, so in that sense, naked rules. But naked's not cozy, so go with thin wool.

Use a minimal bag. Start out with the zipper open, maybe the bag over you, you not even IN it, if it's warm. The VBL works almost immediately. If you find yourself actually sweating, it means you're too hot, and if you're too hot you have two choices: Get out of the VBL, or throw off your bag.

Here's what you need to know about insensible perspiration (and all I know about it, for that matter): It increases (you produce more vapor at a faster rate) when it keeps evaporating, like when it's cold and dry outside. If it's humid outside, you aren't evaporating all that moisture out of your skin, so your body doesn't produce as much. At the considerable risk of insulting you with a picture story, imagine you've got a kettle that you want to fill halfway with water, and keep it there, but there's a hole in the kettle. If the hole is big, you have to pour more water faster into the kettle to maintain the water level. Small hole, less water into it.

Your skin-level moisture is the kettle, and the humidy is the hole in it. High humidity is small hole. That's why when it's humid and you do jumping jacks, you sweat---the evaporation is too slow for the moisture being produced.

So the thing with a VBL is: It increases the humidity level, and slows the rate of evaporation, which slows the rate of moisture production. When an ideal humidity level is reached on your skin and there's essentially no more evaporation (because of the humidity around you inside the VBL, you won't sweat.

You aren't exercising, you're lying there trying to go to sleep, so your body isn't hot from exercising.

Now, if you have too many clothes on, or you have a super thick sleeping bag and it's a 67-degree night, then exercise or no, you'll overheat and start to sweat to cool off. If you do that inside a VBL, it's curtains, mister. The moisture has nowhere to go, and you'll get hot and sweaty and probably blame the VBL. But the VBL has no brain, and your skin has no brain, and everything that's happening is happening because that's how your body works. At that point, it's your own fault for having too much insulation (too little conductive heat loss). So you get out of your bag, out of the VBL, stand outside and let the steam out, then either get back in your bag without the VBL, or get back in your VBL without the bag. Next time, bring a superlight bag and trust your VBL to make up the difference.

There's a rumor out there that VBLs are just for winter mountaineering and super cold temperatures. That's why they were developed, and you'd be nuts to not use one thenn, but they're useful all year around, and they allow you to go three-season camping with minimal gear.

6 feet tall by 32 inches wide. Approx 11oz.

As VBL's go, this is heavy and cheap. But the light ones are 5oz, and most cost a lot more. This one is as simple as can be, one size fits to about 6-4 or so (you don't put your head in it, so don't be thrown off by the 6-ft measurment and the "fits to 6-4" claim. It doesn't come with a stuffsack and doesn't need one. Keep it in your bag and stuff it right along with it. That way you always have it.

If you're a VBL bottom feeder, you'll find that Campmoor has a similar one, lighter, for about the same price. We've got nothing bad to say about that one, wouldn't say it even if we did....but this one here is a really good VBL for a really good price, and a 5-ounce weight difference in a camping load is nothing.

Average Customer Review: 4 of 5 Total Reviews: 2   Write a review.

  3 of 3 people found the following review helpful:
Fix a slippery slope March 26, 2014
Reviewer: Casey Carnes from Grafton, WI United States  
Try using some silicone seam sealer, applied in whatever creative pattern you came come up, inside and outside the vapor barrier to prevent slippage in your bag.  Same thing works great on sleeping pads and tent floors that are slippery.

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  7 of 7 people found the following review helpful:
A love-hate relationship May 28, 2013
Reviewer: George Garber from Lexington, Kentucky  
I'm cheating here, because I don't have a MUSA  Liner.  I have the one you used to sell -- the orange one from Georgia.  But I don't suppose the two differ much in performance.

I can't decide whether I love or hate my vapor barrier liner.  It does exactly what it's meant to do, and on a colder-than-expected night that counts for a lot.   But it's slippery, and that can be annoying.  When using it I have to take extra care to pick a level campsite, or else I'll be fighting gravity all night.  And sometimes I like to lie on my back with my knees bent, but that doesn't work with the liner because my feet keep sliding down.

I take my liner on every trip, and I use it when I need the extra warmth.  But when the weather is mild enough, I'm glad to sleep without it.

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