Fully Enclosed Bivi Bag

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sean_iow
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Fully Enclosed Bivi Bag

Post by sean_iow »

I've got a myog bivi bag that uses a non-breathable base and a breathable upper, which is this material

https://www.extremtextil.de/en/2-5-laye ... hoice.html

It zips up fully but there is a mesh panel in the top, about the size of 2 A4 pages. I taped the seams so it's fully waterproof except obviously for the mesh. I usually have a tarp up if its raining or forecast. I have been caught out in an unexpected shower so thought I'd make a cover for the mesh made out of the breathable fabric. It would be sewn to the bag across the top and then just have some velcro tabs to hold it in place over the mesh.

I may be over-thinking it, but will I be OK or will a lack of fresh air be an issue and there be a build up of CO2?
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benp1
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Re: Fully Enclosed Bivi Bag

Post by benp1 »

I’ve slept with my snowyside borah bag closed. Co2 wasn’t an obvious problem but it felt nicer with a little gap

To be honest being fully enclosed with ok but having some air is much nicer
redefined_cycles
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Re: Fully Enclosed Bivi Bag

Post by redefined_cycles »

I used to have the CO2 issue (or what felt like that) in my army issue goretex thingy. Then the Borah was a little nicer but it did have a massive mesh pocket going across it and...

Anyway, now I've got the Hunka XL (thanks Al) it just seems to have transformed the whole bivy experience ans for some reason feels much more breathable than even the goretex bag. Gone are the days of feeling suffocated and needing to ensure I've manaipulated a careful gap for breathing but not letting in the rain...

Thats what it feels lile to me anyway and each time I use it (once in proper pouring rain so far but slight tree cover and the other times in drizzle) I just can't believe what a bag they've made...

Sorry. ^^ was actually meant to say : maybe I've become less soft over the course of the BAM and not realised (but got carried away thinking of my vaguely exciting Hunka... well done AK if you're listening)...

Shafiq (in case they wish to send me a discount voucher or that new bivy of their thriigh the post :-bd )
ScotRoutes
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Re: Fully Enclosed Bivi Bag

Post by ScotRoutes »

It's not just CO2 that's the problem, it's H2O from your breath.
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benp1
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Re: Fully Enclosed Bivi Bag

Post by benp1 »

What Colin says, humid breath leaving the bag is better

(The snowyside is the event bivy. I also have the normal borah bag that everyone has)
redefined_cycles
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Re: Fully Enclosed Bivi Bag

Post by redefined_cycles »

ScotRoutes wrote: Tue Nov 05, 2019 11:18 pm It's not just CO2 that's the problem, it's H2O from your breath.
This too Colin. It must be that I'm using it in alternate seasons than the others but I usually fully expect the Hunka t wake up with a little puddle somewhere but nope, not even a little. Maybe the cooler weather or something but on the BB200 i both breathed into the bag and slept in my waterlogged woolly thick (HJ Hall I think)socks. 3 hours later and no mini puddle or major signs of condensation at bottom of bag...

I was pleasantly and halpily suprised. :???:
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Bearbonesnorm
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Re: Fully Enclosed Bivi Bag

Post by Bearbonesnorm »

Is the material gas permeable? Just because something is breathable isn't enough.
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sean_iow
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Re: Fully Enclosed Bivi Bag

Post by sean_iow »

Bearbonesnorm wrote: Wed Nov 06, 2019 8:28 am Is the material gas permeable? Just because something is breathable isn't enough.
I don't know if it is,. I think I'll just make a loose flap that can be draped over the mesh when required.

This isn't a modification to be able to use the bag as a stand-alone item in the rain, I'd put a tarp up for those occasions. This is just to keep an unexpected shower or some drips off.

For example, on my January BAM this year the forecast was dry so I just took the bivi to a local woods. I was close to the edge of the woods with open fields beyond. About 5am I was woken by drips of cold water landing on my face. A mist had rolled in across the fields and as it reached the trees the condensation on the leaves was dripping onto me. I only had an hour and a half before I was due to get up. Even if I had the tarp with me I wouldn't have the enthusiasm to get up, put the tarp up and then get back into me bag for an hour. I pulled the upper part of the bag over the opening to keep the drips out but having to hold it in place meant I didn't get back to sleep and just laid there waiting for my alarm to go off :roll: If I had a pre-attached flap of waterproof material I could have just unrolled it over the mesh and gone back to sleep.

I think I make it and see how loose and how much airflow I'm likely to get, I might attach a 'stay' to keep it open at the bottom.
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redefined_cycles
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Re: Fully Enclosed Bivi Bag

Post by redefined_cycles »

Bearbonesnorm wrote: Wed Nov 06, 2019 8:28 am Is the material gas permeable? Just because something is breathable isn't enough.
Thats a fair point Stu... I can only say that it must obviously be their design... Or more probable that I've just gotten better at this bivvying mslarkey without a shelter :smile:
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psling
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Re: Fully Enclosed Bivi Bag

Post by psling »

When you make your flap, make it a little bit longer and put the velcro to the sides. At the end form a hem with a 'stiffener' strip sewn in to the full width of the flap. Fix the 'receiving' parts of the velcro on the bag itself closer together than those on the flap so that when 'closed' you'll have a nice air intake under the stiffener which will be away from your mesh so no drips or light rain on your face :-bd
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sean_iow
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Re: Fully Enclosed Bivi Bag

Post by sean_iow »

psling wrote: Wed Nov 06, 2019 11:29 am When you make your flap, make it a little bit longer and put the velcro to the sides. At the end form a hem with a 'stiffener' strip sewn in longer than the flap is wide.
When 'closed' you'll have a nice air intake under the stiffener which will be away from your mesh so no drips or light rain on your face :-bd
That's pretty much what I've just sketched out :-bd That's the same way the vent on my Deschutes is held open. I'm tempted to use a small stay as it will pack up easier as a full width stiffener will get folded up, this is the way the vents on my Vango work.

I'll mess about with some mock-ups tonight and I once done 'll post some pictures of the finished work.
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Richard G
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Re: Fully Enclosed Bivi Bag

Post by Richard G »

I really want to make my own design bivi bag one day. I have a a general idea for having a sort of spring loaded vent at the foot end, and using kite sticks (poles?) for a sort of hoop to keep the mesh off my face.

Something I'll almost certainly never get around to though.
Thisisnotaspoon
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Re: Fully Enclosed Bivi Bag

Post by Thisisnotaspoon »

Something like an OR Helium bag to give it some volume for the air to circulate?

I've got a Rab Strom which zips up to leave a mesh gap, but it's really humid when zipped up, only really an improvement it's it's reverentially raining. Normally I just flop the top flap over and tuck the bottom flap in a bit so rain runs off.
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Re: Fully Enclosed Bivi Bag

Post by ScotRoutes »

Thisisnotaspoon wrote: Wed Nov 06, 2019 5:30 pm Something like an OR Helium bag to give it some volume for the air to circulate?

I've got a Rab Strom which zips up to leave a mesh gap, but it's really humid when zipped up, only really an improvement it's it's reverentially raining. Normally I just flop the top flap over and tuck the bottom flap in a bit so rain runs off.
Pretty much works for me an my RAB too. Stus micro-tarp would be a good add-on.
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sean_iow
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Re: Fully Enclosed Bivi Bag

Post by sean_iow »

I've added the cover over the mesh area, looks like it will work as required, just enough to keep off any unexpected showers or drips from trees when mist rolls in. There are velcro tabs at the side of the opening and across the bottom. The cover is sewn on across the top and rolled up out of the way.

Image

I put my waterproof inside as it's a contrasting colour as the base is black so otherwise it would be hard to see the mesh.

Image

And with the cover in place. The two front 'struts' are just tubes of the fabric with a thin plastic stiffener slid inside before sewing the ends up. They might move about in use but there should always be some kind of gap to let the air circulate. It probably wont keep a full on deluge out but if that's the weather I'd have the tarp up. The zip around the opening isn't waterproof either so I expect the odd drip inside but at least they wont be landing directly on my face now :smile:
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