Re: [Paddlewise] Drysuits

From: tompage:
> 
>  In a coated suit, you're
> nice and warm too, maybe warmer, when you're paddling, but it would seem
> when you stop paddling, all that soaked clothing around you now acts to
> conduct heat away at a much greater rate than if it were dry, air filled,
> insulating clothing.  Granted, soaked polypro inside a nylon shell is better
> than nothing at all should you take a nasty dip, but Gortex would seem to be
> much superior in performance.

My experience corresponds to your expectations.  I disagree somewhat with Joe
Pylka's analysis, although not with his observations.

When I start a paddleday, my fleece is dry inside my PJ, and I am quite warm. 
At the end of a paddleday (assuming I have been active enough to build up a
good sweat), my fleece is damp, and *at rest* I am not **quite** as warm as I
was at the start of the day, *at rest.*   Still OK, but it is clear the fleece
does not insulate as well.  (Joe and I have about the same experience, I
think.)

Why is the insulation value reduced?  Water, in vapor form, is a better heat
*transfer* agent than dry air. (The physics would bore everybody -- has to do
with its polarity vis a vis nonpolar nitrogen and oxygen.)  The mechanism of
heat transfer exploits the thermal gradient between your (hotter) skin and the
(cooler) inner surface of the PJ.  (Pylka said "no heat gradient to speak of." 
I disagree with that.)  The main reason wet clothing under a water-impermeable
shell still insulates pretty well, as Joe said, is that evapotranspiration is
*not* a mechanism of heat transport away from your wet skin -- because
*everything* inside the PJ is pretty close to saturated with water vapor (and
droplets).  

With *Goretex,* that last statement is not quite true, owing to the slow
migration of water vapor out of the PTFE membrane, and consequent heat loss --
that water was generated as *liquid* when it exited your skin, so the latent
heat of vaporization has to be supplied somewhere to get it to vapor.  That
heat comes from you.  With a totally water-vapor impermeable PJ, there is no
evaporation of *your* moisture from the inside of the PJ to the outside, so the
last statement in the previous paragraph is completely true.

I use Goretex for comfort and because at the end of a paddleday, my fleece is
dryer than it would be under totally-water-impermeable clothing.  I can slide
out of the PJ and avoid switching to fresh clothing.  Saves hassle and I do not
have to maintain two sets of togs on a multiday trip.

-- 
Dave Kruger
Astoria, OR
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