Bivy bags

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Bivy bags

Postby Snafuspyramid » Thu 27 Jan, 2022 8:43 pm

Can anyone recommend a bivy for 3 season use in Victoria (below tree line)? I would use it for short solo trips under a decent sized tarp so I'd prefer something without a membrane.

I'm tall (6'4") and quite heavily built around the chest and shoulders, which seems to rule out some of the Alibaba Tyvek options. I can see Terra Rosa does a Tyvek body with mesh face, interested in whether that is breathable enough.

I have never tried a tarp / bivy but they sound like a popular option in the US, haven't seen anyone use one here yet though. Any sinister reason for that?



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Re: Bivy bags

Postby Walk_fat boy_walk » Thu 27 Jan, 2022 9:03 pm

I use a borah gear cuben bivy with an MLD Cricket cuben tarp (or without in a cave/overhang or in good weather) with a mesh face for 3 season use. It's brilliant and weighs about 100g... roughly 400g paired with the tarp I think.

Edit: no there is no "sinister" reason for their popularity... better than a tent in the right conditions/seasons IMO.

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Re: Bivy bags

Postby Snafuspyramid » Fri 28 Jan, 2022 6:38 am

Hah I was thinking more sinister reason for what seems like the relative lack of popularity here (different Australian conditions for example)...

The Borah Cuben looks like exactly what I was after but the lead times look pretty steep, leaving aside the trouble of shipping anything overseas right now. That is astonishingly light though...

Are there any more readily locally available options? Terra Rosa looks nice (albeit about 100 grams heavier) but I'd still be nervous about breathability on the Tyvek shell.

EDIT: the Borah ultralight bivy looks like it has better availability.

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Re: Bivy bags

Postby Moondog55 » Fri 28 Jan, 2022 8:10 am

Bivvy bags are great as a survival tool, tents are far more comfortable in bad weather, Evans Tyvek bags are sleeping bag protectors/splash protectors and not storm proof.
In good weather you don't need either.
TerraRosa will make an Extra Large splash bag given a decent lead time and they are reasonably good at letting water vapour out as well as being highly wind resistant.
Never used any of the other bivvy bags much and sold on or PIF'd several as my old dinosaur still works
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Re: Bivy bags

Postby wildwanderer » Fri 28 Jan, 2022 9:31 am

Some discussion here.
https://bushwalk.com/forum/viewtopic.php?f=58&t=39148

I haven't used the mesh bivy yet. Its very well made though slightly heavier than spec.

If you have your tarp pitched low splash shouldn't be to much of a problem unless you've got wind blown torrential rain.
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Re: Bivy bags

Postby Walk_fat boy_walk » Fri 28 Jan, 2022 10:08 pm

wildwanderer wrote: splash shouldn't be to much of a problem unless you've got wind blown torrential rain.

Yep although I've also found it useful for condensation in a low pitched (shaped) tarp... can happen!



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Re: Bivy bags

Postby iamkbird » Tue 19 Apr, 2022 11:50 am

So I’m on the tarp, bivy combo train as well.
I use a Z packs hexamid pocket tarp with storm doors and a 3F UL tyvek bivy modified with bug mesh head.
My issue is moisture in footbox and underneath my NeoAir sleeping mat. This happens even when I leave the centre zip undone and my head out.
Three questions
1. I’m assuming it’s condensation or could it be water seeping though the tyvek from wet ground?
2. I don’t use a ground sheet. Would that help? I thought the tyvek would be enough under me to keep water out.
3. Is it just the tyvek not being breathable enough or would it happen the same in a Borah Gear Cuban/Ultralight or similar?
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Re: Bivy bags

Postby Moondog55 » Tue 19 Apr, 2022 12:25 pm

Three questions
1. I’m assuming it’s condensation or could it be water seeping though the tyvek from wet ground?
Yes probably not condensation but water being forced thru by the pressure of your body weight
2. I don’t use a ground sheet. Would that help? I thought the tyvek would be enough under me to keep water out.
Pressure will force liquid water though, when I was using a Tyvek sleeping bag cover I tried to always use a water proof layer underneath me
3. Is it just the tyvek not being breathable enough or would it happen the same in a Borah Gear Cuban/Ultralight or similar?
Sorry I can't answer that as I've never used either, my bivvy bags have always been Goretex but my full Goretex bivvys still needed a waterproof groundsheet when not being used on snow. Soft garment Tyvek is really quite breathable and only water resistant not waterproof IME
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Re: Bivy bags

Postby iamkbird » Tue 19 Apr, 2022 1:40 pm

Thanks @moondog55 that’s exactly what I needed to know. The ground was wet and grassy from 24 hours of rain on my test run so I’ll definitely add my polycro to the kit and retest. When I’ve used this set up in dry conditions there has been no moisture inside but it wasn’t humid or cold.

I do love the extra insurance that a bivy gives me against splash and my bag hitting the tarp in the hexamid. It is bound to happen in a small shelter.
Appreciate your knowledge.
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Re: Bivy bags

Postby Hisham » Tue 19 Apr, 2022 7:30 pm

I've only used a bivy once or twice. I went back to the tent for better weather protection, and you can get tents that are just as light (as a bivy plus tarp) or not far off.

Even in good weather a tent gives you an option to hide from the bugs while sitting up, etc.

I still have my tarp and bivy and might just try it again one day on a walk, but haven't convinced myself yet.
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