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fantasmagris
02-17-2005, 22:40
OK, here's another thought i had. (My daughter keeps telling me to quit putting them out because people have in the past copied them to make money.) Someone may have already thought of this one anyway. Anyway, here's the thought.

Why not make a sleeping bag with a fully waterproof bottom (no insulation there, but a pad sleeve instead) and breathable top, yet with a zip-on fully waterproof "bivy-top!" Seems like it would be perfect for thru-hikers or anyone else who was looking to use shelters or sleep out under the stars and only rarely would be forced to sleep thru a rainstorm. Sure, there would be condensation issues when the bivy-top was zipped on, but no more than with any other bivy. However, it seems for the true minimalist it would eliminate the need to carry either a ground cloth or shelter. All you would need is your bag, pad and "bivy-top!"

:-?

Mountain Dew
02-18-2005, 01:30
Simple, because they would be marketing that idea to all of about 100 people world wide. Nice idea, but much more thought and creativity it will take to become reality.

WhiteMtns
02-18-2005, 12:23
Wouldn't seem too difficult.

My hammock design keeps evolving until it has integrated under insulation, and a built in top quilt. Hammock and sleeping bag in one. Still under a tarp for shelter...I like the idea of having a tarp to use with or without the hammock/bag. But Waterproof shell is not impossible. shelter, bed, and bag all in one. Now attach shoulder harness and hipbelt to the underside of the hammock - a la moonbow powerpack - and eliminate backpack. Big three all integrated to the Big one. Pack, Sack, and Shelter. Going a bit too far???


Along the lines of what you're heading to...it's not hard to make an ultralight bivy slip cover. Tyvek bathtub for the bottom, and wtb on top. No groundcloth...eliminates one piece of gear...but the insulation isn't yet integrated the way you are heading.

your design wouldn't be so hard to construct...but I still would want a tarp with it...don't trust that WTB shell material if there might be standing water.

fantasmagris
02-18-2005, 12:44
Intended it more for thru-hiker use in shelters (insurance against blowing rain, drips, etc.). Heavier silnylon floor under pad, lighter silnylon for zip on top.

Just seemed logical to me since you don't generally want a WP barrier over insulation. Why not zip-on, zip-off...?

Already made 6 oz bivy/bag cover w fully WP bottom and gossamer breathable top. Thought about adding insulation under top, but decided would reduce verstality. It's a great warm weather sleep on top (of bag) cover as is.

Yeah, tho i'm not a hammcok camper (yet), I did also think about a "hang-able sleeping bag" which I guess is just another name for an insulated hammock. Would have to deal with venting issues tho.
:D

WhiteMtns
02-18-2005, 17:07
that's another reason for all breathable materials...and a decent silnylon tarp

Streamweaver
02-26-2005, 11:40
I think the main reason they dont make many bags with waterproof fabrics is that they will slow the drying process down considerably when the bag gets wet.even a bag made with sil nylon could eventually get wet given enough rain/snow and once that happens it would prolly take so long to dry that it would be mildewed ,stinky and heavy.Just something to think about. Streamweaver

hungryhowie
02-26-2005, 12:48
Actually, the reason you should never incorporate a waterproof breathable, much less a waterproof non-breathable fabric like silnylon, into a sleeping bag is that it will prevent the transfer of the mositure emited by your own body. The human adult body emits 3 pints of moisture each night. And while the majority of that is through the mouth/nose, a considerable amount is still emitted through the skin. If you have a waterproof top on your bag, the moisture will have no place to go. It may take a week, but your sleeping bag will be useless, down or synthetic (tis a little known fact, as DuPont has more capitol to spend on marketing, but synthetics only retain MORE of their insulative properties than down when wet...about 65% v. about 40%...not that big of deal really. Kinda makes you wonder about all of those syntehtic sleeping bag fanatics who think they'll die if they touch a down bag, but I digress). And yes, you could unzip the waterproof layer and let the bag air out every morning, but your asking your customers (or yourself) for an additional 30-60 minute committment every single day, and if it rains for extended periods as it is prone to do on the AT, your just out of luck.

-howie

plodder
02-26-2005, 17:26
Howie, Excellent points. What about vapor barrior liners, which are popular?
Some people like synthetic because its easier to launder than down, and you can wring it out, unlike down, which will help you keep warm if your bag is wet.
Or have feather allergies. Or do that vegan thing.

Groucho
02-26-2005, 23:10
The human adult body emits 3 pints of moisture each night. And while the majority of that is through the mouth/nose, a considerable amount is still emitted through the skin.
-howie
Way too high. You'd be doing overtime to get rid of a pint.

hungryhowie
02-27-2005, 11:58
Howie, Excellent points. What about vapor barrior liners, which are popular?
Some people like synthetic because its easier to launder than down, and you can wring it out, unlike down, which will help you keep warm if your bag is wet.

VBLs go on the inside of the bag. They prevent the moisture from ever getting into the bag in the first place, hence they will not cause a problem. They can get really clammy because of this, however.

-howie

hungryhowie
02-27-2005, 12:01
Way too high. You'd be doing overtime to get rid of a pint.

Well, I haven't done any extensive testing, but that was a statistic given to me by a MSR rep from back in the day. It includes moisture through the mouth and body over an 8 hour period of sleep. Even if it's not 3 pints, you can't argue that when you wake up in the morning in an unvented tent there's a god awful amount of moisture on the ceiling. That's a lot of stuff that you DON"T want on the inside of your sleeping bag.

-howie

cutman11
02-27-2005, 12:48
In hospitalized patients we sometimes need to keep track of their fluid balance and measure all inputs and outputs. Normally 750cc of "insensible" losses are added to the outputs to cover sweating and air vapor from breathing. When on respirators with humidified gases, the number is more like 250cc. That of course would be at room temp and with a controlled indoor %humidity. So if you double that for the outdoor, cold, dry air, 1.5liters (or 3 pints) would be about right, with 2/3 of that via breathing. If you keep your face out of the bag, that would leave about 500cc loss into the bag, or 2cups. Take out your vapor barrier liner, put 2 cups of warm water in it, and then climb in. You will feel pretty wet i'd bet.

ronmoak
02-27-2005, 13:49
Why not make a sleeping bag with a fully waterproof bottom (no insulation there, but a pad sleeve instead) and breathable top, yet with a zip-on fully waterproof "bivy-top!" Seems like it would be perfect for thru-hikers or anyone else who was looking to use shelters or sleep out under the stars and only rarely would be forced to sleep thru a rainstorm. Sure, there would be condensation issues when the bivy-top was zipped on, but no more than with any other bivy. However, it seems for the true minimalist it would eliminate the need to carry either a ground cloth or shelter. All you would need is your bag, pad and "bivy-top!"

One variation or another of that idea has been around and marketed on and off for the last 30 years. In '77 my summer bag on my thru-hike was very similar in concept and sold by REI. It had a coated taffeta bottom, pad pocket and Polarguard insulation on top. The only difference was the top cover wasn't waterproof. Gortex was still in the lab at that time.

In '96 I made three bags using patterns I made from ripping apart my '77 bag. These had coated ripstop bottoms, pad pocket, Thinsulate fill and Ultrex W/B tops. The bags were good for temps into the 30's and worked great in tarps. Today you could save a lot of weight building the same bag using better lighter materials.

Today, bags like the Big Agnes and Top Rab try do similar things with varying degrees of success.

Ultralight bivies are good for extending the usefulness of bags without W/B shells and keeping your bag clean. They may even add a few degrees of warmth. However, there are certainly lighter more cost effective alternatives.

A simple down quilt with good W/B shell and a silnylon ground cloth. It's lighter just as effective and more versatile.

I do disagree with HungryHowie on one point. That is the effectiveness of W/B materials when used as shell material in sleeping bags. While he advocates avoiding them, I preach the opposite. Iíve used and recommended them on even on synthetic fill bags. My opinion is that keeping your insulation dry is paramount for long term safety and comfort.

One thing Iíd like to keep clear is that weíre talking about 3 season backpacking here. The notion of VBL really doesnít apply, even though itís frequently mentioned. In sever cold situations a Vapor Barrier Liner is also critical for keeping your insulation dry. Without it the moisture will freeze inside the insulation and canít be easily or effectively removed. Also to be very effective a VBL should be close to the skin. Such as the VBL clothing offered by Stephenson. Used outside of your clothes itíll do little more than soak your clothes making your life even more miserable. If we're talking about Alpine mountaineering or polar exploration then this would be more appropiate.

I've got over 4 years experience using the Epic fabric from Nextec in my sleeping bag. It has preformed flawlessly in a wide variety of environments. Including hours spent in a soaking wet collapsed tarp then entering town the following day when the only dry thing in my pack was the down in my sleeping bag.

One can certainly speculate that these types of shells will inhibit the flow of moisture escaping the bag. However, Iíve yet to see and documented scientific evidence backing it up. I believe that itís far more important to keep your insulation dry from water coming through the outer shell, than to worry about the potential for buildup from sweat. Believe me there are few people on this planet that sweat more than me.

During the normal course of your daily hike, you can generally find a couple of hours of sunshine when you can layout your sleeping bag to air it out and evaporate any moisture build up. Having a black interior will help speed this process.



Fallingwater

Groucho
02-27-2005, 15:16
Well, I haven't done any extensive testing, but that was a statistic given to me by a MSR rep from back in the day. It includes moisture through the mouth and body over an 8 hour period of sleep. Even if it's not 3 pints, you can't argue that when you wake up in the morning in an unvented tent there's a god awful amount of moisture on the ceiling. That's a lot of stuff that you DON"T want on the inside of your sleeping bag.

-howie
I had a much longer response typed for my original post, but something happened and it was lost and I didn't have the ambition to retype at the time.

3 pints per 8 hrs is 9 per day; that is 4.5 qts, a gallon and a pint. It is recommended that 64 oz. of fluid be injested for a day! That's a large deficit even without accounting for urination, etc.

The Hammocker
02-27-2005, 15:38
I got an idea......

Instead or putting so much thought into it get one of those big trashbags
and just put it over your sleeping bag pad under the sleeping bag and if you
really want slip a hammock into the mix.

cutman11
02-27-2005, 17:22
Groucho -- I stand corrected. My numbers would be in a 24 hr period. So for 8 hrs in the bag, it would be 1/3 that amount, or 2/3 of a cup. Still, put that much warm water in a bag and get in.....

hungryhowie
02-27-2005, 18:04
Ron,

I must admit that I've never used Epic. so I can't really comment on its effectiveness, but after using Dryloft bags I can say with certainty that they do trap more moisture than a simple 1.1oz (or 0.8oz) breathable nylon with DWR. I don't have any scientific evidence to back it up, nor do I have the disposable income to complete such a study, but long term use of each type has taught me that the more breathable the shell, the fewer times you'll need to let it air out.

In my experience, dryloft bags really need to be aired out for 15-30 minutes after each night of use to keep them "crisp" and lofting well, while I can count on one hand the number of times that I've needed to air out my bags with breathable shells.

But like I said, maybe Epic really is that much better.

Still, I doubt that you'll disagree that it is your shelter's job to keep the weather off of you, and your bag's job to keep you warm. For me, at least, using a dryloft or epic shell is more weight, cost, and trouble, especially when my cheap homemade silnylon tarp ought to be keeping the weather off of me in the first place.

-howie

ronmoak
02-27-2005, 18:53
Still, I doubt that you'll disagree that it is your shelter's job to keep the weather off of you, and your bag's job to keep you warm. For me, at least, using a dryloft or epic shell is more weight, cost, and trouble, especially when my cheap homemade silnylon tarp ought to be keeping the weather off of me in the first place.-howie

Years ago when I first stated going down the road of Ultralight I adopted the "Systems Theory" to gear that Ray exposes. For a long time I felt that was simply enough to answer all my questions when deciding on which gear to select. Over the years Iíve come to see that while itís a good starting place, itís also incomplete. Iíve augmented it with some additional theories to better explore the subject.

One of them is what I call the ďTheory of ElasticityĒ. The lighter the system and the more you push it to its extreme, the more elastic the system needs to be. Otherwise when one component fails, the system will collapse, sometimes with disastrous results. For the most part, we donít really stress ultralight systems, even though people frequently bemoan the apparent inherent risk of ultralight. Risks that are far more mental than physical in most cases.

In shelter systems, the elasticity starts at the macro environment and runs through to the micro environment, ie everything from sight selection to ground cloth. An elastic system is one in which there are built in redundancies within each component. Now I realize that this may appear to run antithetical to normal ultralight wisdom. However, if you think about it, itís really what ultralight is all about.

I recommend W/B shells, because while they may weigh an ounce or more than other shells. They also provide a greater degree of protection in the system at whole and allow for a greater range of options such as smaller tarps or different ground cloths.

Anyway itís just something to think about, when nothing else is going on!

Fallingwater