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Moisture Management in Goretex footwear

BACKGROUND

Gore-Tex is designed so as to allow moisture vapor to escape through the protective membrane, but to prohibit water from entering from the outside.  In this way it is effective in managing moisture when the feet perspire and in inhibiting “reverse osmosis” of water through the boot.

Gore-Tex lined leather footwear, while designed to afford maximum protection for the feet in field and combat operations, does, however, present challenges in quick drying. Of particular concern is what occurs when the boot is fully submerged (as in stream or river crossings) and water enters the boot and saturates the footwear.

In order to optimise moisture management, however, a good boot is not enough. Rather, a system of footwear protection, including an engineered sock product and a well designed boot can enhance protection and comfort and manage moisture much more effectively.

Outdoor apparel applications have proven many times over the concept of “layering.”  Layering as a means of managing moisture and providing effective insulation is accomplished in a “systems” approach in which a base layer of non-absorbent synthetic fibres close to the skin wicks away liquid moisture. Through a thermal gradient that “moisture” is transported through a preferably breathable insulating mid layer (if necessary) and then through the membrane of the outer layer to the outside of the shell.

The effectiveness of this process is compromised if the breathability of the outer shell is reduced through the surface fabric “wetting out”. Regular washing of the shell and then treating with Durable Water Repellent (DWR) enhances breathability and thus inhibits the overloading of the membrane through its reduced capacity to “breathe”.


THE SYSTEMS CONCEPT IN AN OUTDOORS BOOT 

Using the layering approach to optimise moisture management, the first wicking layer in the boot (next to the skin and fat pads of the feet) is an engineered padded sock product.  This sock product, for maximum effectiveness, should be a man-made fiber or blend of man-made fibers (acrylic or polyester).

The engineered padded sock product moves moisture away from the foot and to the next layer – the lining of the boot.

From the lining the moisture then moves through the GTX lining and into the upper of the boot where it can evaporate.


NOT ALL SOCKS ARE CREATED EQUAL

Sock products made from man-made fibers wick moisture away from the feet through special “channels” created in the fibers during the extrusion process.  Socks made from natural fibers (i.e. cotton and wool) cannot wick the way man-made fibers can because they do not have these channels.  In fact, natural fibers are hydrophilic: In the closed environment of a boot or shoe, cotton and wool absorb and retain moisture.  This absorption and retention causes the fibers to collapse and to lose whatever protective characteristics the socks may have.  Wool is especially absorbent, capable of absorbing up to 30% of its weight.2

Man-made fibers such as polyester and acrylic are hydrophobic: they actually repel moisture. Some man-made fibers are more effective than others in providing protection for the foot. Polyester fibers such as CoolMax have superior wicking characteristics, but offer less resiliency and protection. Acrylic provides both high wickability and high resiliency and protective capabilities. The superiority of acrylic in protection against blisters has been proven in peer-reviewed published research studies [see footnotes 3 and 4 below].

The Thorlos Clinically Tested Padded Sock (CTPS) hiking sock and other outdoor styles are of high acrylic content. In addition, the proprietary THORLON acrylic yarns have special profiled channels that more effectively wick moisture away from the feet.

Even in situations where the fabric becomes saturated (as in river or stream crossings), the acrylic provides protection for the feet because, even though it may become saturated by the water around it, the fibers do not ABSORB the water and thus retain their resilience.


DRYING OUT LEATHER BOOTS WHILE IN USE

Modern boot constructions consist of multiple components (as many as 180 components per pair) amongst which are linings which may be textile (Cambrelle, Dri-lex etc.), leather, Gore-Tex (GTX) along with padding between the lining and the upper.  

Our belief is that boots with GTX linings along with engineered padded socks from man-made fibers will dry out more quickly than either leather or textile lined even when the boots have been filled with water. In those circumstances (assuming there is no other river crossing imminent) we recommend removing the boots, tipping out the excess water and wringing out the socks.

From the discussion above with appropriate wicking socks (which are hydrophobic and don’t absorb water) the thermal gradient along with the pumping action of the foot inside the boot will force the moisture through the GTX membrane which as said acts like a non return valve. In the case of boots like a LOWA GTX Boot the moisture will then migrate through the ventilation channels between the upper and the padding/lining and exit through the perforations on the scree cuff or through the tongue, up the shaft of the boot as well as through the upper itself so long as the pores of the leather are not totally clogged with foreign matter and excessive wax.

The uppers of the boots (like GTX shells in outerwear) should be also treated with LOWA Water Stop (or similar) which acts like DWR to aid the process and avoid wetting out the surface. With activity within a relatively short period of time the feet should be substantially dry even if there is still some accumulated moisture outside of the membrane and the padding and the uppers are still wet.


A FINAL WORD ABOUT CLINICALLY TESTED PADDED SOCKS AND BOOTS USED AS A "SYSTEM" 

Activity specific socks such as say a Thorlos Hiking sock, or Combat Boot sock (made predominantly from Thorlon acrylic yarn) sock are specifically designed to complement outdoor boots and enhance mobility and maintain foot health under demanding backpacking/trekking, training and even combat conditions.

They achieve this through:

- Exclusive Thorlon construction for resilience, durability and better wicking;

- Thick cushioning in the ball and heel to reduce pressure and impact forces[2] and to reduce shear force and the incidence of blistering[3] [see footnotes 3 and 4 below].

- Moderate cushioning over the instep protects against abrasion and boot pressure;

- Moderate cushioning in the arch for better fit and comfort;

- Thick cushioning aids in boot fitting of mismated feet and acts like a fitting gasket. The padding will compress where it needs to and remain uncompressed elsewhere acting like a space filler to optimise the fit particularly on the smaller of the two feet.

In the event that it is desirable to introduce a wool blend to suit colder conditions, a Wool/Thorlon Acrylic blend is optimal. This blend combines the warmth and insulating characteristics of wool with the wicking and resilience of Thorlon Acrylic. This blend allows the sock to provide warmth, move moisture and to retain the resilience to reduce the impact and shearing forces and assist in lessening the incidence of blistering.


CONCLUSION

Moisture management, and thus comfort and protection, are enhanced by using a layering “systems” approach to footwear consisting of an engineered padded sock and high performance specially lined GTX outdoor boots.  Research has demonstrated the effectiveness of CTPS sock products made from man-made fibers, in protecting against pressure and shear forces, consistent with superior moisture management.

The best way to protect the feet of active outdoors people is by use of the proper Boot/sock system using Thorlos Clinically Tested Padded Socks.


[1] It should be noted that Polypropylene is a non wicking fibre

[2] Characterization of Liquid Moisture Transport Performance of Wool Knitted Fabrics, Zhou, Liya, Feng et al, Textile Research Journal; December 1, 2007.

[3] Use of Experimental Padded Hosiery to Reduce Abnormal Foot Pressures In Diabetic Neuropathy, Veves, Masson, Boulton et al, Diabetes Care, Vol 12, No 9, October 1989

[4] Friction Blisters and Sock Fibre Composition, a Double Blind Study, Herring & Richie, Journal of APMA, Vol 80 No 2, February 1990