[sleep systems] Liners for Down Bags..?

The real beauty of a vb liner is it keeps your bag from absorbing moisture in below freezing temp.
Somebody else probably can tell you the correct term but we exhale h2o which is absorbed by down or synthetic bags and reforms ice, frozen water is a really poor form of insulation.
This is usually not a problem on overnight trips but anything longer it is.
A vbl will add about 5 degrees of warmth and it will keep your bag drier.
If you are trying to compensate for a real difference in temps either more clothing, which can translate into less room inside the bag or possibly less loft if it is tight, or an overbag.
If you use a vbl you do need to turn it inside out and shake/break the moisture accumalation on longer trips,just let it freeze and it will slough right off.
Every vbl I’ve used does feel a little strange but if you think about it so does the nylon shell.
There were some vbl’s out there that had a kind of flocking to compensate for this but they weighed a ton.

I have a WM ULtralite on the way and I purchased a Cocoon Silk liner for it. It claims to add 9.5 degress of warmth and weights 4.7oz. It might be something else to consider as it sells for only 40 dollars.

I general don’t recommend a VB until it’s closer to 0F cause I find them too stuffy in warmer temps. I found that a good VB (at least in colder temps) gave me somewhere between 10-20F of extra comfort. Just remember if you use a VB to wear at most a ultra-light base.

I have also used silk liners. They do add a bit of warmther. I think it’s closer to 5F than the claimed 10F. A silk liner can be a bit help in keeping your bag clean, but I think there are more efficent ways to stay warm. Namely wearing extra clothing. A light down and synthetic vest can keep you warm in the morning and evening as well as providing warmth when sleeping.

–Mark

I have a thermalite reactor liner and love the thing, it may not be for the ultralite’s since it weighs 8oz, but claims to add 15 degrees to a bag.

I slept great this weekend in my Montbell #7 in 40 degree weather when it’s rated at 50 degrees.

http://www.rei.com/online/store/ProductDisplay?storeId=8000&catalogId=40000008000&productId=47687834&parent_category_rn=40003719&vcat=REI_SEARCH

REI considers 13oz ultralight? http://www.rei.com/product/11435609.htm

DO NOT BELIEVE Sea to Summit’s claim that its Thermolite liner can boost a bag’s temperature to anywhere near 15F! The bloody thing is so thin it reminds me of women’s stockings — you can pretty much see through it! I’ve used this thing before, and I’d say that it provides about a 5F boost — at most.

Aside from my own experience — which is of course subjective…

1. I’ve read other people’s complaints about the Thermolite.

2. MontBell sells a hoodless bag that can be used alone or as a liner. Even though this bag is 725 fp down (!), MontBell only claims a 10F boost.

Your success in “extending” your No. 4 MontBell bag from 50F to 40F is much more likely a combination of your own bag’s capability — with a small assist from the Thermolite.

A lot of posters have commented on using a set of down or synthetic undies to complement and augment a bag’s temp rating. I can attest to that with my MB UL #4. It is rated to a comfort level (higly accurate IMHO) of 37 degrees. By adding a MB UL down jacket and pants I have been able to move it down to about 25 with no tent on a still night. Inside a tent I have had this combo down to 20 and have been very cozy. Under the down garments I have worn a set of REI silk LJs and off course a possum down cap. I assume one could do the same with the Thermawrap set, too. The added benefit is that you can hang out in camp wearing these garments and still be warm as the temps drop. The same goes for the early morning visit to the tree.

I just don’t know how anyone adjusts to these liners. Seems to me that they would be subject to shifting and twisting. I don’t want to be fighting my bag in the middle of the night.