Vapo barriers, condensation and bivies

"The tightly woven cotton is called Ventile, and is used in the damp UK and in the Antarctic. Heavy though.
Uncoated nylon? Ugh!"

Being from the damp UK I can say that Ventile isn't used much for backpacking here. Day hiking yes, because a double Ventile jacket (weighing 2+lbs) will keep you dry in several hours of rain. However it needs drying somewhere warm if it's to keep you dry the next day. I've had a few unpleasant experiences with wet Ventile jackets! If wet Ventile freezes it becomes very stiff – very windproof but uncomfortable. A wet or frozen Ventile jacket is very heavy too, as it absorbs so much moisture.

Uncoated nylon doesn't absorb much moisture of course and dries much, much faster than Ventile. How comfortable it is depends on the type of nylon. Pertex is uncoated nylon.

For cold conditions, damp or dry, I prefer Paramo waterproof clothing, which is as breathable as Ventile but waterproof and fast drying. It's also very comfortable. I have fallen asleep in my sleeping bag wearing a Paramo jacket and trousers – waking in the middle of the night because I was too hot.

As to vapour barriers I've found both vapour liners and clothing effective but never very comfortable. As I haven't had problems keeping down sleeping bags dry even in cold weather for trips of 2-3 weeks, the longest I take in winter, I stopped using VBs.

Michael, sorry I missed this question. I have not seen the breakdown between lungs and skin. If I run across something in my websurfing, I'll post it.

A theoretical exercise puts a little more lost by respiration, during sleep.

http://advan.physiology.org/cgi/content/full/29/4/213

Stephenson makes several statements about physics & physiology without offering anything to back them up aside from stating that he was trained as an engineer & so, presumably, understands basic physics. You also make statements about physics & physiology without offering any backup references, so why should anyone believe you any more than Stephenson?

"Please don't put vapor barrier clothing over your face. It will suffocate you."

The guy who doesn't have enough common sense to follow this one wins the Darwin Award.

My reference here was Guyton's Textbook of Medical Physiology for the numbers and some older articles on others…mixed in with my own opinion occasionally.

The articles about vbl's on this site and Andrew Skurka's are very good and avoid the bizarre claims that Stephenson makes.

I notice no one has mentioned the ol' VBL half shirt. This solves the soaking of the "warmth" layer due to sweat and your pack laying on your back as the pack is acting essentially as a waterproof barrier.

Take a "normal" base layer shirt, long sleeve generally, as its cold though I also wear it quite often up to 50F or so, and "paint" the back where your pack rests on said shirt making it waterproof. Silicone works and is easily dissolvable using mineral spirits for an even light easily available solution. A rubberized paint works as well though hard to find.

This lets the front breath and vent while your "back" has VBL meaning you won't sweat out your back under your pack at least in regards to your warmth layer which in my case is powerstretch 100 fleece followed by a wind shirt generally. Or its a long sleeved shirt and a wind shirt.

VBL socks/gloves are essential and DO NOT LEAVE HOME WITHOUT THEM! Makes life so much more enjoyable. Turns a "cold" 40 degree night into a toasty warm night. Keeps the boots DRY, no more ICKY, or less anyways, ICKY super cold boots in the morning. Tennis shoes or equivalent for extended periods of time on snow is plain stupid unless its high summer time.