COLD INJURIES - Medicine for Mountaineering and Other Wilderness Activities - page 392

Effective cold weather clothing must have two properties: insulation and permeability.
Insulation basically is the ability of the clothing to entrap air and prevent convective heat
loss. The insulating properties of a material are dependent upon its thickness and how well
it inhibits the movement of air. Permeability refers to the ability of water vapor to move
through the fabric. Water vapor resulting from the evaporation of sensible or insensible
perspiration on the skin must be able to move through clothing to the atmosphere. If the
clothing is impermeable, the vapor condenses and the clothing becomes wet.
A variety of natural materials are used in clothing for outdoor wear. Wool, cotton, silk,
and goose down are the most popular. All but down are usually combined with synthetic
materials such as nylon, polypropylene, polyester, and acrylics to impart specific desirable
characteristics to the fabric.
Underwear
Polypropylene became popular for underwear in the 1970s. Because it is hydrophobic
andallowsmoisturetowickfromtheskinsurfacetothesurfaceofthefabricwhereitevap-
orates without cooling the skin, it provides a greater sensation of warmth. Furthermore,
polypropylene retains most of its insulating properties when wet. The disadvantages of
polypropylene include its retention of body odors—it can become quite foul after repeated
use—itstendencies tobecomebrittle whenheatedandtopillwhendriedinaclothesdryer,
and its tendency to become baggy. The last problem has been corrected to some extent by
adding nylon to the fabric.
Polyesterfabricshavetoalargeextentreplacedpolypropylenebecause,inspiteofbeing
slightlymoreexpensive,theydonothavethesamedisadvantages.(Capilene®,Coolmax®,
Thermax®,andThermostatarethetrademarksofpolyesterfabrics.)Thesefabricskeepthe
skin cool and dry through a wide range of activity, but to achieve this effect they must be
worn next to the skin, not over cotton underwear or as a jacket.
Woolremainsanexcellentfabricforunderwearbuthasfallenfrompopularityandisdif-
ficulttofind.Addingasmallamount(atablespoon)ofoliveoiltothewashwatercanelim-
inatethescratchinessthatwooltendstodevelopafterrepeatingwashings.Merinowoolhas
much finer fibers and feels more comfortable against skin.
Somepeoplelikethefeelofdrysilk,butwhensilkbecomeswetitfeelsunpleasant.The
fabric holds 25 percent of its weight in water.
Insulation
Wool is the oldest and one of the best insulating materials for cold weather clothing.
Its major disadvantage is its greater weight than pile or fleece, but it is still popular for
caps and gloves. Wool is one of the few materials that maintains its insulating properties
when wet. However, with prolonged wetness the inner core of wool fibers can absorb