bivvy bag

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Sweep
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Re: bivvy bag

Post by Sweep »

Barks wrote:As mentioned above, goretex type bivvy bags are only ‘breathable’ when they are dry, once rain or heavy dew is on them condensation will quickly build up inside and you will get very clammy and cold - Goretex type material is not the wonder material that many people think it is. The army system uses a shelter sheet to keep the worst of the moisture off and the bag itself keeps the wind off and warmth in. As for the mat, if you have a Thermarest neoair inflatable type then keep it inside the bag (it is more expensive than the bivvy bag in any case and can easily puncture) and use a ground sheet (a piece of builders Tyvek works very well) to minimise risk of sharp stones, briars or thorns damaging the bag itself. If you use a closed cell foam mat then that can work well underneath but there still remains a tendency to roll off it. Army bivvy bag plus shelter sheet plus tyvek groundsheet still come in at around nearly 1kg and will cost under £100 if you shop around. Ultra lightweight tents can come in at around 1.2kg with poke system and will cost at least over double that but you do get an encllosed space away from bugs and better protection in very bad weather. You can also get very lightweight mesh inner tents that will go under a shelter sheet that are much more comfortable than bivvy bags and more versatile. DD Hammocks are a good site to look at to get the idea with lots of informative instructional video clips of the different options.

Yes a lot of truth I think in your comments about condensation. I slept in my army bivi in a wood once, September or October. No rain that I was aware of. But the next morning my sleeping bag was rather seriously wet/damp on the outside. Luckily I had stopped just short of my intended campsite, so I just laid the bag over the farm gate to dry in the sun. I do have a tarp/shelter but need to work on the set-up. Your post gave me the kick I need. Thanks.
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mercalia
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Re: bivvy bag

Post by mercalia »

Sweep wrote:
Barks wrote:As mentioned above, goretex type bivvy bags are only ‘breathable’ when they are dry, once rain or heavy dew is on them condensation will quickly build up inside and you will get very clammy and cold - Goretex type material is not the wonder material that many people think it is. The army system uses a shelter sheet to keep the worst of the moisture off and the bag itself keeps the wind off and warmth in. As for the mat, if you have a Thermarest neoair inflatable type then keep it inside the bag (it is more expensive than the bivvy bag in any case and can easily puncture) and use a ground sheet (a piece of builders Tyvek works very well) to minimise risk of sharp stones, briars or thorns damaging the bag itself. If you use a closed cell foam mat then that can work well underneath but there still remains a tendency to roll off it. Army bivvy bag plus shelter sheet plus tyvek groundsheet still come in at around nearly 1kg and will cost under £100 if you shop around. Ultra lightweight tents can come in at around 1.2kg with poke system and will cost at least over double that but you do get an encllosed space away from bugs and better protection in very bad weather. You can also get very lightweight mesh inner tents that will go under a shelter sheet that are much more comfortable than bivvy bags and more versatile. DD Hammocks are a good site to look at to get the idea with lots of informative instructional video clips of the different options.

Yes a lot of truth I think in your comments about condensation. I slept in my army bivi in a wood once, September or October. No rain that I was aware of. But the next morning my sleeping bag was rather seriously wet/damp on the outside. Luckily I had stopped just short of my intended campsite, so I just laid the bag over the farm gate to dry in the sun. I do have a tarp/shelter but need to work on the set-up. Your post gave me the kick I need. Thanks.


thats interesting . i used my alpkit bag around march 2017 temp outside about 6C and no such problem
crazydave789
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Re: bivvy bag

Post by crazydave789 »

mercalia wrote:
pjclinch wrote:
Sweep wrote:
Sorry only just spotted this.

How does that happen Dave?

Honest question.

As above, I do prefer the mat inside - I did use it outside to start with but I had a habit of moving off the thing during the night. I also figured that the Thermarest was also more likely to get mucky, wet or worse if ouside. I stress that I don't transport the mat inside the bivi.


If the bag is on the mat it'll protect the bag from any roughness on the ground. If the mat's inside the bag is against the ground. Mats tend to be both relatively tougher and static while bags move if the sleeper is mobile, but which one is against the ground will be more prone to damage, so you choose, you lose...

I'd think it's on the list of "things to be aware of" rather than "don't do this because"

Pete.


well mats on the ground can thus get pricked and leak. rather than happen to the bag. unfortunatley my Thermarest mondo king is too big to go in my bag, as other wise it would be put there at it aint cheap at £120+ these days


all the punctures I've repaired on our thermarests have been on the top not the bottom oddly enough. chair kits certainly help.
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Re: bivvy bag

Post by Barks »

Mercalia wrote:
thats interesting . i used my alpkit bag around march 2017 temp outside about 6C and no such problem

It’s not really about temperature, iinternal condensation occurs within goretex type materials when the outside is wet or when the environment humidity is really high. These materials work best in cold dry conditions that maximises the difference between that and the warm moist interior of the garment or bivvy bag surrounding your body.
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Si
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Re: bivvy bag

Post by Si »

Procrastination is one's friend.....took me so long to decide which other bivvi to buy that Alpkit have the one i originally want back in stock! Hopefully it'll arrive before the weather turns (and before the solstice :wink: ).
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Re: bivvy bag

Post by pjclinch »

Barks wrote:Mercalia wrote:
thats interesting . i used my alpkit bag around march 2017 temp outside about 6C and no such problem

It’s not really about temperature, iinternal condensation occurs within goretex type materials when the outside is wet or when the environment humidity is really high. These materials work best in cold dry conditions that maximises the difference between that and the warm moist interior of the garment or bivvy bag surrounding your body.


Yup. And of course, in cold, dry conditions there's no great need for waterproofing, and one is probably better off without it...

Goretex et al are not at their best when you actually need them, because physics :( (having said that, they're still a whole lot better than emergency poly-bag bivvis. I've never spent the night in one of those but I've seen people who have get up in the morning pretty well soaked)

Pete.
Often seen riding a bike around Dundee...
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Sweep
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Re: bivvy bag

Post by Sweep »

Si wrote:Procrastination is one's friend.....took me so long to decide which other bivvi to buy that Alpkit have the one i originally want back in stock! Hopefully it'll arrive before the weather turns (and before the solstice :wink: ).

Would be interested in your views on this when it arrives, and after you have field tested it.
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Re: bivvy bag

Post by Pastychomper »

pjclinch wrote:
Goretex et al are not at their best when you actually need them, because physics :( (having said that, they're still a whole lot better than emergency poly-bag bivvis. I've never spent the night in one of those but I've seen people who have get up in the morning pretty well soaked)

Pete.


For a long time I used an army bivvi which was almost as breathable as a polybag, and yes condensation was one of the two problems with it. The other was it was too small. Eventually I gave up and replaced it with a single-skinned one-man tent from Lidl, which I still think of as a bivvi bag with a frame.
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Sweep
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Re: bivvy bag

Post by Sweep »

Pastychomper wrote:
For a long time I used an army bivvi which was almost as breathable as a polybag, and yes condensation was one of the two problems with it. The other was it was too small. Eventually I gave up and replaced it with a single-skinned one-man tent from Lidl, which I still think of as a bivvi bag with a frame.

Was the army bivi goretex?

Surprised that it was too small. Not the sort of thing I expect from the army.
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Re: bivvy bag

Post by Barks »

pastychomper wrote:
I gave up and replaced it with a single-skinned one-man tent from Lidl, which I still think of as a bivvi bag with a frame.
.

But even with single skinned tents condensation can often a problem that has to be taken into account. All these approaches are about matching your needs to the compromises you are prepared to deal with, there is no universal solution. I use a tarp and lightweight mesh inner (to keep bugs at bay) from late spring through to autumn using a tent when weather conditions are likely to be more extreme, particularly in mountains where high winds and driving rain are more likely. The good thing on a bike is that weight is less critical than when backpacking so even using a two skinned tent is a reasonable option if you want the extra comfort and space. My bivvy bag (army goretex version) is now only taken on day trips as an emergency shelter, it is a bit heavier than a poly bag but only by a couple of hundred grams.
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Re: bivvy bag

Post by Pastychomper »

No, the bivi bag wasn't Goretex, it was a thin plastic-coated fabric, dyed olive green. It was quite robust for its size though. When I say "army" I mean it was bought from a government surplus warehouse and didn't appear to be one of their more 'civilian' products, but it's anyone's guess who originally specced it. :) The size would have been fine for someone up to maybe 6' tall but I'm a bit longer than that and like to stretch out.

Barks wrote:But even with single skinned tents condensation can often a problem that has to be taken into account. All these approaches are about matching your needs to the compromises you are prepared to deal with, there is no universal solution...


+1 to that. My tent mostly avoids condensation by being better ventilated than the average bag but I suspect that will have its limits, plus I fully expect it to convert into a loose bivvi bag if it's ever exposed to a gale. It's fine for backpacking though, and can fit nicely on a bike.
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crazydave789
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Re: bivvy bag

Post by crazydave789 »

pjclinch wrote:
Barks wrote:Mercalia wrote:
thats interesting . i used my alpkit bag around march 2017 temp outside about 6C and no such problem

It’s not really about temperature, iinternal condensation occurs within goretex type materials when the outside is wet or when the environment humidity is really high. These materials work best in cold dry conditions that maximises the difference between that and the warm moist interior of the garment or bivvy bag surrounding your body.


Yup. And of course, in cold, dry conditions there's no great need for waterproofing, and one is probably better off without it...

Goretex et al are not at their best when you actually need them, because physics :( (having said that, they're still a whole lot better than emergency poly-bag bivvis. I've never spent the night in one of those but I've seen people who have get up in the morning pretty well soaked)

Pete.


the orange bags are purely emergency and make lousy bag covers if you are a tad sweaty.

survival wise the best way is to cut off a corner and climb in head first to maximise heat retention.
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Si
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Re: bivvy bag

Post by Si »

It arrived today - a day too late for the solstice....will have to wait a while before I test it. But, shock, horror, a bit of camping kit that fits EASILY into it's own stuff sack...a miracle!
mercalia
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Re: bivvy bag

Post by mercalia »

Si wrote:It arrived today - a day too late for the solstice....will have to wait a while before I test it. But, shock, horror, a bit of camping kit that fits EASILY into it's own stuff sack...a miracle!


did you get the small or large one? The small one must be very small. I got the large one and is hardly massive
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Re: bivvy bag

Post by crazydave789 »

Si wrote:It arrived today - a day too late for the solstice....will have to wait a while before I test it. But, shock, horror, a bit of camping kit that fits EASILY into it's own stuff sack...a miracle!


faulty - send it back.
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