Vapor Barrier Liners: Why Trapping Moisture Backfires
THE MYTH ABOUT VAPOR BARRIERS
The following information I found on the internet on a website “SECTION HIKER”. Some of the information I suspect is good and some not so good, such as what follows.
“Western Mountaineering is a manufacturer of outdoor gear. They produce a vapor barrier sleeping bag liner called the Hot Sack VBL1. A vapor barrier liner (VBL) works by stopping heat loss from evaporative cooling. A VBL will also prevent your body vapor from degrading your insulation. This is most important during extended stays inside your bag2.
A VBL works by stopping heat loss from evaporative cooling. A VBL will also prevent your body vapor from degrading your insulation. This is most important during extended stays inside your bag. The Western Mountaineering Hot Sac VBL goes one step further by stopping radiant heat loss with its reflective metal coating. This proprietary fabric is a new lightweight ripstop.”
Vapor barrier liners are made from waterproof materials. When you are in one the moisture from your body does not get out. It does not stop heat loss via evaporative cooling. THAT IS A MYTH. The moisture in the VBL become liquid and you become clammy. Because you are wet when you get out of your sleeping bag and consequently the VBL you get an instantaneous chill. Think about getting out of the shower, same affect. The VBL does not stop radiant heat loss. THAT IS A MYTH.
All the VBL does is keep your moisture from getting to the down which if it does will be absorbed by the down which will then lose any heat retention in the bag that it had.
The following is from Feathered Friends.
“The Cocoon Expedition Ripstop Silk liner is a great addition to a cold-weather trip, as it provides a little boost in warmth for the colder sleepers. The Expedition liner takes the brunt from any nighttime perspiration, so it is easier to hang up and dry.”
The fabric is made from silk fiber which is highly absorbent. The liner is said to take the “BRUNT” of any nighttime perspiration. The reality is that the silk material is absorbing your moisture, which then is absorbing your body heat all night.
Using their bags means you have to have the VBL in order to make them work better does not happen; things get worse as you can see.
This problem with down as an insulation in sleeping bags has existed since they were first made, in the 1930’s I believe. I could not find in my research when VBL’s were first employed.
As I have said many times moisture from your own body is your enemy. You can get a “SLEEPING BAG” [WIGGY’S BAG] that is unaffected by moisture and allows without question the moisture from your own body out, so you stay dry and warm.