Bivvy Bags

21 May 2015 16:18 #63892 by andrew r
Replied by andrew r on topic Bivvy Bags: 2015 Update
Resurrecting this thread in the hope of getting fresh info on the use and availability of bivi/bivy/bivvy bags: what do YOU take with you and when? Is it just for survival, or do you multi-task it?

My core motivation for asking is that I'm in the process of upgrading my sleeping bag and was wondering how to keep it in top working order; obviously a liner inside helps to keep the inside clean and a bit warmer (depending on the liner), and it makes sense to me that in caves (draughty/dusty/dirty) that some kind of removable, cleanable 'outer' makes good housekeeping sense; obviously it needs to be breathable to prevent/limit condensation, and if it is waterproof too it's suddenly become a bivi bag B).

Next question: If you're carrying a tent then does a bivi bag become superfluous, or do you allow for the possibility that your tent gets blown away?

I'd be glad to read your thoughts...

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21 May 2015 20:08 #63897 by ASL
Replied by ASL on topic Bivvy Bags
I'm in the market for a bivy bag since I had a very wet night in Mponjwane Cave. Survival bags suck (officially!).

I like fast and light trips using caves but carrying no tent and doing big distances introduces risk. I doubt I would ever carry both but the bivvy bag provides a lot of security and will certainly protect my sleeping bag in damp caves.

B)

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21 May 2015 20:21 #63898 by ASL
Replied by ASL on topic Bivvy Bags
PS. I did some research on bivvy bag performance. There are some detailed studies that you can Google.

The basic outcome of what I found is that eVent is by far the most superior fabric and very few bags are breathable enough to avoid moisture build up. Most bags are reinforced on the bottom for waterproofing purposes and one study recommends getting a bag which is eVent top and bottom. Ironically Goretex is not a top performer in any study.

For our climate I think eVent is a must...
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21 May 2015 21:16 #63900 by sibr
Replied by sibr on topic Bivvy Bags
I've always been very interested in them. Bit to expensive just to buy one to see how it works. I recently did a berg trip with 3 people. One tent is too little but taking a second one seemed too much. A bivvy would have been perfect.

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04 Jun 2015 11:27 - 24 Oct 2015 13:53 #64131 by andrew r
Replied by andrew r on topic Bivvy Bags
I got a quote for 20m x 1.5m Tyvek HouseWrap (61g/m2) and 25m Tyvek Adhesive Tape in order to make a home-made bivy bag, but it works out to R400 (per bag) to make 4 large bags (could make 5 if we make them a bit smaller), which is a bit costly to try on a whim.

I noticed recently that CapeUnionMart have an emergency bag made out of something that looks like Tyvek for about R350, I think it weighs something like 150g and folds up about the size of a baked bean tin, so I think I might give that a try first.

Edit: I bought one of these CapeUnionMart emergency bags on sale, will report back when I have tried it out.

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Last edit: 24 Oct 2015 13:53 by andrew r. Reason: Update 21 Oct 2015

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04 Jun 2015 11:43 #64133 by spook
Replied by spook on topic Bivvy Bags
I have done most berg trips without tent and always take a bivvy bag for additional security if we don't get the cave, the cave is wet or we sleep out.

I have a 20y old Salewa bivvy bag with a breathable upper and thicker hard wearing lower surface. It still works fine and has saved my butt from many a miserable night.

The most notable I remember was in Pins Cave when the drip over the front became a torrential waterfall during the night and we would have been soaked to the core without bivvy bags. The storm raged all night and we witnessed one of the most spectacular light shows ever.

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04 Jun 2015 16:57 #64142 by ASL
Replied by ASL on topic Bivvy Bags
I think breathable fabric is critical as I have found survival bags to be a nightmare with my down bag. Whatever fabric you try, my suggestion is Google its breathability. My other thought is that if there is no spec for it don't bother because things aren't well engineered by mistake :ohmy:
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05 Jun 2015 11:51 #64150 by mike
Replied by mike on topic Bivvy Bags
I have a Black Diamond twilight bivy that comes with me on most trips. I very seldomly take a tent especially if I know the area and caves. It really small and folds up to a coke can size at 300 odd grams.
I have experienced some moisture issues on warmer nights but in the same breath it does keep you dry.
It takes some getting used to but when fully zipped in with the hood open but meshed closed it breaks that chill from the wind on your face, never had to sleep completely zipped in though.
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08 Jun 2015 14:29 #64168 by intrepid
Replied by intrepid on topic Bivvy Bags
I have used my own Cape Storm bivy bag, as well as my wife's MSR E-Bivy for sleeping out in the open and in rough overhangs in the Berg. Unfortunately they both tend to form a lot of condensation on the inside - unless, in the case of the Cape Storm bag, it is a seriously cold, dry, mid-winter night. Basically I can only use these when it's really needed (ie raining or snowing), in which case its better to get a bit wet on the inside. I have yet to find a bag that works well for me.

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23 Oct 2015 15:44 #65503 by Papa Dragon
Replied by Papa Dragon on topic Bivvy Bags


Bivy bag. The blue fabric is silicon impreg nylon, completely waterproof. Green panel is untreated nylon, completely breathable. I intend to attach a panel of water repellant/breathable fabric 100mm larger on each side over the green panel. I had thought of either velcro, or press studs.
Also thought of making a panel that is completely waterproof, that would also be detachable. That might get very wet inside though.
Any thoughts, snags, input or advice please?
Thanks

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