Sleeping Bag, bivvy, liner combos etc...

Hi all,

Couple of questions about sleeping bags, liners and bivvy bags coming up. Done quite a bit of reading/searching and nothing of this type came up...

But first, my particular situation. I've got a relatively heavy and bulky (2.4kg/5.2lbs) synthetic bag (allegedly rated to -5c) that i use in a bivvy bag when out in winter with a tarp (A-frame/open ends/open sides) as a cover. I'm looking to reduce the weight/bulk whilst obviously keeping the warmth and i was thinking of reviving my old Field & Trek down bag (1.8kg/3.0lbs) in its place - it's a moonlite model incase anyone might dig up any info on it ;-)

The bag was bought in '93 and has been stored for the majority of it's life in it's stuff sack. I know this isn't good for it but due to space constraints, open and bulky has never really been an option. When bought it was a decent bag and is 1100gm duck and goose down - that's all the label says, i can find nothing about it on the web and F&T do not have any info. It doesn't appear to be dirty (the down's not clumpy) but obviously the loft had gone from it - after running it in a large dryer for 15 minutes it did loft out a bit. Should i try getting it professionally washed/dryed?

To begin with i'll be using it just a few nights at a time, and it'll be stored inside the bivvy, inside a pack liner (mostly waterproof) in my pack so it should be pretty well protected from the elements. I slept out in 5c with the tarp, bivvy, a 3/4 cell-foam mat+thin silver insulating mat on top and a silk liner, clothing wise just underwear & tshirt and it was warm enough. Head was outside the bivvy with a merino hat on and although slightly cold in a breeze i expect a balaclava/neck covering would remedy that.

So some questions i have about the old bag, using a down bag in a bivvy etc -

#1) How much insulation/effect would a down bag like this lose over this time and how comparable (generally) would it be with a synthetic model as described above?

#2) If i were to do this often (down bag in bivvy) would condensation be enough of an issue to worry about with regard to it getting wet and losing its insulation properties? I'm thinking it'll be okay after my test at 5c. It will not get any time for an airing during use.

#3) Are liners really any good? Apart from keeping the bags cleaner do they live up to the expectations of adding enough warmth to justify the extra weight? And how do silk liners compare to fleece or to specialised liners like the Sea2Summit reactor thermolite? Or as i carry light thermals would putting these on negate any benefit from one?

#4) Conditions i'm expecting to encounter are probably rarely going to go lower than -5c although i would want to be able to manage to be comfortable if temps are at that level or should temps drop further - how much extra range would you expect items to give you?

a) Wearing thermals inside the bag
b) A reflective item on top of a foam-mat
c) Emergency blanket


Thanks for any info,

Lewis.

From my own experience--silk liners add little or nothing to the warmth of the bag. While using it I would be so tangled up by morning that it would take me several minutes to get out of the sleeping bag.

For conditions below freezing, a vapor barrier liner inside your bag is good. It keeps the moisture from your body ("insensible perspiration") from going into the bag and freezing when it hits the outside shell, which can compromise your insulation. If your bivy is not highly breathable, you're going to have condensation inside it, which will also compromise your insulation. The vapor barrier liner will help with that, too. However, you don't want to be using the vapor barrier in above-freezing temps, because it becomes a sauna!

I've never had too much of a problem with condensation inside down from me (i.e. having the down wet out) due to frost in it
until I get down to very cold temperatures. (well, something like -10 to -15C and below. If it's above that I tend not to worry about it too much. If you do have to worry about it, a vapor barrier liner will work (as OM mentioned) if you can stand to sleep in them. If you can't you can use a synthetic overbag - the goal here is to keep the line of freezing outside the down bag, so the frost collects in the synthetic overbag. Works for me.

Thanks - i'm not too worried about get caught up in the liner. For me, i found that it help me turn inside the bag easier! I think i will keep it if only to try and keep the bag clean though.

Anyone any thoughts on either of the queries on how much less efficient a bag would be after being stored like this for that period of time and also how much warmth other items (like thermals & reflective items) provide?

Off this weekend so will soon find out if condensation/getting the bag wet is going to be a problem!

Cheers,

Lewis.