Bivvy bag to boost sleeping bag.

[BigMonster]

Hi guys I need some advice on bivvis as I have never done it. I have a synthetic sleeping bag with 0C upper comfort rating (-6C lowert comfort) and I have been thinking how could I extend that if temps drop below 0C as I'm a cold sleeper.
1. Liners are not an option as I hate the tangling when I need to go pee, I rather sleep in extra layers.
2. I will never use that bivvy above 0C as I like my freedome of movement.
3. The only bivvy I can find would fit me and my XL sleeping bag (and my budget) is Alpkit Hunka XL.

So how many C's would one gain wrapping up in a bivvy?
What would be the condensation situation below 0C?

Any thoughts much appriciated.

 

[Broch]

I have slept out in my ex-army gortex bivi bag in sub-zero temperatures (i.e. woke up with frost on my face and frozen ground) with just a three season sleeping bag - but I couldn't give you any temperature figures I'm afraid. I got mine from M&G for about £30 but I don't think they have them any more.

 

[Philster]

I find a bivvy helps by preventing the wind stealing the heat from your bag - an ex-army goretex bag is cheap, huge and will suffer no condensation problems, forget the Hunka which is a bit of a sweat bag.
The bivvy gives you an extra layer of air around you to insulate you - couldn't say a figure but I definitely notice the difference

 

[Nomad64]

https://bushcraftuk.com/community/index.php?threads/army-gortex-bivy-bag-new.148688/

 

[crosslandkelly]

A bivvi bag will normally add a season to the rating of your sleeping bag. This is a rough guide only.

 

[Nice65]

Hi guys I need some advice on bivvis as I have never done it. I have a synthetic sleeping bag with 0C upper comfort rating (-6C lowert comfort) and I have been thinking how could I extend that if temps drop below 0C as I'm a cold sleeper.
1. Liners are not an option as I hate the tangling when I need to go pee, I rather sleep in extra layers.
2. I will never use that bivvy above 0C as I like my freedome of movement.
3. The only bivvy I can find would fit me and my XL sleeping bag (and my budget) is Alpkit Hunka XL.

So how many C's would one gain wrapping up in a bivvy?
What would be the condensation situation below 0C?

Any thoughts much appriciated.

Have a word with Greg about the Army ones he has.

The main drawback for me, particularly with the hammock, would be getting in and out. I've opted for a central zip DD bag. Wriggling into a sleeve of Goretex defeats my aim, I'd do it for wind protection only. And have a pee bottle handy.

 

[MikeLA]

Wouldn’t use anything else except for the Brit issue one now tried the hunk a XL and it was still too narrow. Used to do a lot of bivvying without a basha, even in winter in th Cheviots.

 

[Erbswurst]

I have a Goretex bivvy from the british army, 800 g, and a Snugpack Special Forces bivvy bag, 340 g, which I usually use together with the SF 1 sleeping bag.

Since I bought the Snugpack SF system I stopped using the heavy one. It is working as good as the Goretex bivvy, but is simply so light, that I use it in summer conditions too. The zip offers enough ventilation to use it 4 seasons.
I use it on a foldable insulation mat from the German army to protect it.

It is existing in two sizes, one up to around 185 cm and one far larger.

The oliv green ist cheaper than the camouflage patterns.

How much a bivvy can add to the comfort temperature depends on the wind.

Without any wind, in a double wall tent, perhaps 3 *C or 5*C.

If the wind is blowing, and you are in the open field, your sleeping bag keeps this temperature. Without it looses its performance.

I never would go any more in conditions lower than 25*C without my Snugpack SF bivvy anywhere.

And with 340 g (in the packing size like an apple) there isn't any reason to leave it at home. That is the difference to the heavy and bulky military bivvy.