Warmth Boost with VBLs and Down

I’ve played with VBL a little but found that they don’t add very much warmth.  Any other insulation is much warmer for the weight

But, I’ve read that VBL is good for multi day trips in cold weather, like 0 F.  Your body produces sweat which flows out through your insulation layers.  The temperature inside the insulation drops from 95 F or so at your skin to ambient outside the sleeping bag.  At the point the temperature inside the insulation goes below freezing, the flow of sweat vapor flowing through it will freeze.  After doing this for a few days, the sleeping bag will accumulate a lot of frost which will inhibit it’s insulation value and it will weigh a lot.

If you go into conditions like this – multi day and cold – then you should have a VBL to prevent frost from building up in you sleeping bag.  Like if you’re on a polar expedition.

https://www.warmlite.com/vapor-barrier/ describes in more detail.  Stephenson was an early proponent of VBL.

So, VBL isn’t for warmth (although it adds a little) but is good for preventing frost in your sleeping bag

pretty much what jerry said.  I found that on the first night (before I had to worry about condensation in my insulation) that a vapor barrier added something like 5F degrees of comfort to my bag.

I think with a vapor barrier you don’t typically want to wear much in the way of clothing because now you are trapping that moisture inside. You would probably want to layer the down over the outside of the barrier, but inside your sleeping bag.

I bought some “fuzzy stuff” from warmlite and made a base layer shirt and pants.  That worked pretty good.  Then. I could wear any insulated jacket/pants outside it and not get them wet

The warmlite concept is (was?) to have the fuzzy stuff VBL on the inside of the sleeping bag.  Then, wear nothing inside of that.  Thus, the catalog with naked people (mostly women).

I am a mysoginist pig man that enjoys looking at pictures of naked women, but I kind of object to making your women employees pose naked for a catalog, supposedly to illustrate that you shouldn’t wear anything inside the VBL, but I have to think it was mostly just to be outrageous and satisfy men’s desire to look at naked women.  Maybe I’m wrong. Maybe Stephenson actually didn’t like women or know that that would sell merchandise.