Re: Vapor Barrier shirt material?

BenSimms-aF9gUBWsH8U@xxxxxxxxxxxxxxxx wrote: 
> Somebody please explain to me the theory behind "Vapor Barrier" 
clothing.  
> How would keeping moisture trapped inside your clothes do anything 
but make 
> one damp and uncomfortable?  In winter, this could even be 
dangerous as it 
> would increrase thermal transmission from your body to the cold air.

Hi Ben, 
The idea behind vapor barrier clothing is that skin prefers to have a 
certain definite amount of moisture content in the air surrounding 
it. When this moisture evaporates, the skin will pump out more 
moisture to replace the lost moisture. However, if you capture the 
moisture and do not allow it to escape, the skin will stop producing 
moisture once it has that optimal amount around it. 

It works better for some than for others, due probably to both 
physiological and psychological differences between individuals. If 
you think you are cold and clammy due to the vapor barrier, then you 
probably won't be happy using them. They do feel "different."

Some people never are able to really be comfortable with vapor 
barriers, others are able to get along with them even when hiking or 
skiing, and still others can only tolerate them while they are in 
their sleeping system. You can experiment inexpensively with vapor 
barriers if you already have non-breathable rainwear, which can act 
as a vapor barrier very nicely.

NOTE to Bryan; for a vapor barrier system you definitely need non-
breathable material like silnylon or coated nylon.  Best,  Don L.