doctoral thesis

DOCTORAL THESIS- FOOTWEAR FOR COLD ENVIRONMENTS-THERMAL PROPERTIES, PERFORMANCE AND TESTING

Recently I wrote that the Army published a sources sort notice looking for a new combat cold weather boot. I contacted them and asked if they had a basic temperature rating for the boot. I received a very interesting and informative reply. You see I asked for a temperature rating in Fahrenheit, however they wrote back giving me the definition of “clo” since that is what is noted in the notice.

CLO- does not refer directly to a temperature range, but instead is a measure of thermal insulation. In general, the higher the clo value of a boot, the greater will be the warmth provided by the boot in a cold environment. Therefore, as I understand it the thicker the insulation the higher the clo will be; okay so the thicker the insulation the greater the heat retention, but that is a fallacy. As you will see it will be explained why.

They also referred me to the thesis, titled above which I found fascinating since it has a significant amount of wonderful information also as you will see. It was published in 1999 and written by Kalev Kuklane from Lulea Tekniska University and published by National Institute for Working Life. They are located in Sweden. I am very grateful that they made me aware of this thesis.

What Mr. Kuklane has done is compile information from studies as far back as 1948 and ending in 1999. Most of the studies referenced took place from the late 1970’s through the late 1990’s.

There was no mention but once of clo and not one mention of waterproof breathable.

EFFECTS OF COLD

The primary control center for thermoregulation of the human is the hypothalamus. The input to the hypothalamus from temperature sensitive nerve endings (in toes) is decisive for the intensity of heat production.in a cold environment, this control system will try to maintain thermal balance. Conservation of heat is achieved by thermoregulation. It is brought about by a reduction of blood flow to the surface (skin) and a counter current heat exchange between arterial (blood moving from the heart) and venous blood (blood moving back to the heart). For example, under cold conditions the arterial blood enters the foot at a temperature of about 86 degrees F. when cold receptors are excited, more heat is produced by increasing the metabolic rate and heat is diminished by decrease in peripheral circulation in order to preserve thermal homeostasis of the central part of the body. (This means that blood is withheld from going to the feet by vasoconstriction). This causes cooling of the extremities, which will diminish muscle power and performance since a considerable proportion of the muscles are situated in the legs. It also reduces skin blood flow causing a loss in sensitivity. (When I was lost I experienced frost bitten fingers and ever since when it gets cold I now know why I cannot feel the cold once it gets below 30/35 degrees, blood not getting to the skin of my fingers).

FEET IN COLD

The extremities are more affected by the cold exposure compared to other parts of the body. The hands and feet have surface area which is very large in relation to their volume. Due to the unfavorable surface to mass ration of human extremities these parts suffer exceptionally high rates of heat loss. Extremities have little local metabolic heat production because of their small muscle mass. (Our muscles are the heat producers in our body and our food is our fuel, and the colder our body experiences the faster we consume our fuel i.e. our metabolic rate increases). Our feet are in frequent contact with cold surfaces more so than the other parts of our body. This further explains why the extremities are more affected by cold exposure, they are the first parts to be affected by chilling and it is where the results of chilling are most acute. No matter how warm the rest of your body is, if you have cold and wet feet you will still be uncomfortable.

Their testing showed that rapid heat loss occurred via evaporative heat loss. The feet sweat and that moisture trapped in the boot was absorbing the heat very quickly. If a person will generally feel cool he will often notice it in his feet. Cold feet may actually be a symptom of general cold discomfort.

EFFECT OF SWEATING ON THE THERMAL INSULATION OF FOOTWEAR

Often the cold sensation in the feet is connected with low skin temperature due to sweating and moist feet. The footwear can be well insulated, but when getting wet, whether do to an outside or inside source, the feet start feeling cold. Dry fibers and sir between them are good insulators. The problem occurs when, air in and between fibers is replaced by moisture. Water conducts heat about 23 times better than air.

While the thesis is 94 pages long I believe I have highlighted the primary information. The bulk of the thesis discusses the many test methods on various machines which are of no interest to me.

What I received from the thesis is a confirmation of why my Lamilite boots and socks perform so well. As I have said feet sweat enormous amounts of water compared to the rest of the body and being farthest from the heart it is essential that one be dressed for the cold environment they are going into which will keep blood flow to the extremities at its warmest, and then of course having footwear that that does not retain the moisture.

I wonder what the Gore marketing people would say if they were to read this thesis. I wonder if one boot manufacturer has ever read the thesis. I wonder if anyone in the Army responsible for cold weather footwear has ever read the thesis since they told me of its existence. In my opinion I believe the answer is NO. There is reference to foot ailments to include trench foot as well. Also, when people are doing work and they experience cold feet they have accidents because muscle movement throughout the body is compromised. I did not think about it during the time I was lost in the blizzard but rest assured I have since then know how fortunate I was to have the Joe Redington mukluks on because if not for them while the rest of me was warm my feet would most certainly have frozen and if found I would have lost them.

The next time you find that you are in need of new boots think very carefully if you really want a boot that has a label on it that states “waterproof and breathable” and if you happen to buy them remember only wear them in July because if you wear them during the winter months I guarantee you will have cold feet.

If you want to read the entirety of the thesis just type into a search engine the authors name and the title of the thesis.

Also remember that Lamilite/Climashield continuous filament fiber insulation is not only second to every other insulation material in the world because it makes every other product out their obsolete.