Bivi Bag advice needed

[Wayland]

I'm looking into getting a Bivi Bag for the Arctic trip next year as I think my old Ventile bag cover won't really be up to scratch.

For cold conditions do you reckon it's better to have a bag big enough to put the mat inside (in this case a Downmat) or have the bag just around the sleeping bags with the mat underneath it?

 

[Twodogs]

use a large Thermarest ridgerest under the bivi bag mate have a look at this below ,

http://www.hikinginfinland.com/2009/12/gear-talk-sleeping-pads-mattresses.html

the site well worth a look really

The dutch bivi bags a good with the L zip very user friendly plus theres straps below to retain the mat , made under lience for carinthia in Spain

Twodogs

 

[Radix lecti]

My personal choice is to leave the the mat underneath the bag,i seem to sleep better that way.


Darren

 

[Twodogs]

Or get your plundered richs and buy one of these,
http://www.youtube.com/watch?v=34jTeP1j_M8

You know you want one

Twodogs

 

[Sniper]

If you are on snow or ice it should be fine as little chance of "punctures" but perhaps a closed cell mat to lay underneath the downmat for safety if not.

 

[Shewie]

I always put my mat inside so I can't roll off it in the night

 

[Wayland]

I have to admit my first thought was to enclose the mat to hold it in place but I'm worried about the excess space required in the bag to do that.

In sub zero conditions the danger is that the water vapour reaches dew point before diffusing out of the bag resulting in condensation and then possibly frost formation inside the bivi bag. My instinct is that this will be less likely in a closer fitting bag.

My choice so far is between the Brit army bag which would take the whole caboodle or the Dutch bag with the mat outside.

I doubt if the retaining band on the Dutch bag will fit around the down mat unfortunately without modification.

 

[markie*mark0]

I always put my mat inside so I can't roll off it in the night

+1 thats what i do, stops waking up cold and realising you've rolled half way through a forrest hahaha

 

[BobvanVelzen]

The dutch bivy fits any 51 cm mat snugly. In the service we were tought to put it inside to protect it, and not to loose it in an unforseen hurry (run away).

 

[sandbender]

I always put my mat inside so I can't roll off it in the night

This is what I have done and for the same reasons.

"...I doubt if the retaining band on the Dutch bag will fit around the down mat unfortunately without modification..."

If it is really cold in the morning, -30 or colder, you want something straightforward and simple that you can either secure to the back of your pack or quickly cram into it, having everything inside a decent bivi bag provides for this. The sooner you are up and moving the better, you will already have to dress and put your boots on, you don't want to be deflating mats and rolling up sleeping bags too.

Thats my feeling anyway.

 

[torc]

In the last few days of the freeze last winter I stayed out for a night in my Arktis tunnel bivvy.
In general I'm pretty happy with this bivvy but I have no experience with any other model of tunnel bivvy to compare it to.
This was my first time using this type of bivvy in prolonged sub-zero conditions.
I zipped the bivvy completely closed.
I normally do this when it's chilly and have never had a problem.
This time the condensation froze to the inside of the MVP membrane and a thick layer of hoar frost formed outside the bag.
I awoke smothering and fighting to get the bag's zipper opened.
What ever type of bivvy you choose remember that the air permeability will be greatly reduced when the membrane freezes.
Happy trails...torc.

 

[sandbender]

"...I zipped the bivvy completely closed...This time the condensation froze to the inside of the MVP membrane and a thick..."

I have only completly sealed myself into a bivi bag to avoid insect attacks, otherwise my face is always outside, even in a snow trench at -40. Keep your face outside, the stars are nice to look at and condensation build up is negligable.