How Heat Loss Works and How Insulation Stops It
Here is my observation of how best to stay comfortably warm in cold conditions. Controlling heat loss is primary to staying comfortable. But first what exactly is insulation? Dead air is what insulates!
If you place polyester fiberfill or down between two materials the air that is trapped within the fiberfill or down does not move because air sticks to any surface for a distance of 1/8 th of an inch. If you break up the air within the 1/8 th inch to smaller increments it is still harder to move it so it stagnates. Stagnant air like stagnant water will retain the heat that it receives and insulates, not the actual material. The material is the catalyst and the difference between the polyester and the down is that the polyester does not absorb the moisture that it is exposed too while the down does.
There are 4 primary actions that take place and two of them are in my opinion not very important so I will mention each of them first. But before that an explanation of what constitutes warming the earth needs to be explained.
The sun light that hits the earth warms the earth. It is this solar radiation that the earth receives that is absorbed by the clouds, oceans and land masses. All of these objects then heat the air. The air is not heated by the radiant heat directly. The air around us is heated by the objects that absorbed the sun’s rays. When the earth is exposed, it is dark; i.e. soil and dark objects absorb heat, it will absorb the sun’s rays and heat up and the heat that the earth has absorbed will rise and heat the air it is coming in contact with. That is how the air is heated, not by the sun directly. All dark objects that are exposed to the sun’s rays absorb the heat in that manner and then heat the air that is in contact with the objects.
People of the desert always wear white clothing because the sun’s rays are reflected away from the white surface. During the summer months in Antarctica the snow and ice do not melt in the interior of the continent because the sun’s rays which hit the surface of the continent for 24 hours a day do not melt the snow, the rays basically bounce off of the white surface, snow, and are reflected back into space. What does melt is the ice and snow around the perimeter of the continent because the water is absorbing the sun’s rays, heating and that heated water is heating the ice and causing it to melt. Also note that the melting takes place under the ice, not on top, because the white surface is reflecting the sun’s rays back into space.
When we have large snowfalls on the ground you can see that the snow begins to melt along the edges where it is next to uncovered ground. As soon as an opening appears in the snow and the ground is exposed the opening gets bigger also from under the snow because the dark ground is absorbing the sun’s rays and warming so that warmth is causing the snow to melt. Since dark colors absorb heat that is the reason all of the cold weather bags I make are black and the rest are made with dark colored fabrics. Did you ever put your hand on the exterior of a black car in summer? It is hot because the dark surface has absorbed the radiant heat from the sun. Do the same to a white car and it is cool to the touch. Generally people who live in warm climates like the southern part of the USA will buy white cars for this very reason.
RADIANT HEAT
Radiant heat loss is for all intents not a factor of any consequence. Radiant heat which the human body produces just like the sun is always absorbed by the first solid object that it hits, just like the objects that the sun’s rays hit. If you are active and the temperature is 80 degrees F your core temperature is 98.6 degrees. As your core temperature increases due to your activity your internal body temperature increases and automatically sends the excess heat to your skin surface. Along with the heat coming off of your skin surface; which is radiant heat, there is moist vapor coming out of your pores which is also warm. This vapor will condense coating the surface of your skin which absorbs the heat on the skin surface and cools your body; this is because the moisture is absorbing that heat. The heat coming off of your skin surface is radiant heat which is being released into the air. Now if you are dressed and the air temperature is 40 degrees F your body is still giving off radiant heat only now it is being absorbed by the fabric; i.e. the object covering your body. It does not travel any further away from you. If you are dressed for temperatures as low as -40 degrees F again you are giving off radiant heat but the loss getting outside the layers of clothing is again non-existent, therefore radiant heat loss is not to be considered.
CONVECTIVE HEAT
Convective heat loss or heat loss via convection is the second action of no consequence. Convective air movement occurs when air is heated and it rises. Some examples are the heat coming off of a candle, heat rising off of a radiator or the reason glider pilots like to fly over black top parking lots especially in Arizona during the summer; the sun’s rays heat the black top; the air contacting the black top is warmed; the warm air rises and cooler air that is sinking moves in to take the rising airs place and as it warms from the black top surface it to rises, and this cycle continues until the earth’s surface, black top cools. This convective air movement is so aggressive glider pilots can hit altitudes of 40,000 to 50,000 feet. Do you think the human body can generate that type of heat? Of course not! Therefore, it is not necessary to consider convective heat loss as a detrimental action either with respect to the human body losing the heat it is producing.
EVAPORATIVE HEAT
Evaporative heat loss, however, is a concern. Moist heat leaving the human body can be a very serious problem when it is trapped next to the skin surface. The human body is constantly giving off moisture through the pores. This moisture has a very specific purpose, to cool the body as internally it heats up. When the air temperature is 80 degrees F and you are active the sweat glands produce lots of moisture. That moisture then acts as a conductor, removing the heat from the skin surface cooling your body and it is then conducted to the air. If you are active when the air temperature is 0 degrees F and you are dressed for the condition and you are sweating and the moisture has no place to go outside of your clothing, once you stop the activity the moisture cools down quickly and cools your body quickly as well. You now experience a chill.
The cooling action of the moisture, demonstrates how efficient water is at absorbing heat. Actually water is the most efficient absorber of heat on the planet. The word insulation comes directly from the Latin word “insular” pertaining to island. Islands are generally warmer than the main land because they are surrounded by water. The water is absorbing the sun’s rays keeping the island warm or insulating the island.
CONDUCTIVE HEAT
The final method of heat loss is via conduction. Conductive heat movement is when an object is heated such as a cast iron skillet. The heat from the skillet travels to the handle and consequently you need some form of protection when you grab the handle. When it comes to clothing that is insulated, the purpose of the insulation is to trap the heat that the human body gives off. As the heat travels away from the body which is the source of the heat it heats the first layer of clothing it comes in contact with which in turn heats the second layer which in turn heats a third layer. The heat is being conducted away from you and if the insulation is not efficient at stopping or reducing the rate of conduction the heat movement is not slowed. Therefore, the insulation that you use to surround your body should not be a good conductor of heat.
The combination of evaporative heat loss and conductive heat loss is what we are dealing with. I have mentioned that water in any of its three forms is the greatest absorber of heat on the planet and it moves the heat via conduction. Water in any of its forms; liquid, solid, or vapor is a conductor of heat. From the study of physics we know that heat moves to cold. If you are in a humid cold environment the moisture in the air even though you do not see it is conducting the heat from your body away from you. Having grown up in New York City (NYC) I know firsthand how cold it can get because of the humidity factor. Now living in Colorado I can be dressed in less clothing for the same temperatures since the humidity factor is 10 percent versus 80 percent in NYC. Over the years as I was learning about insulations and how they perform I read all of the explanations and theories from a scientific perspective. What I did not read was from a practical application. The science references the thickness of insulation for a given temperature condition. That is not necessarily accurate once you begin to learn the differences between the different insulating materials and how they are formed into a useable state.
Gerry Cunningham the founder of Gerry Products that was established in 1946 in my opinion was the original authority in the outdoor industry on “How to Keep Warm” which was the name of a booklet he wrote and published in 1971. The basic information was very valuable to my understanding of what it took to be warm. Generally speaking his booklet discusses in detail all of the methods by which we lose heat, how we produce heat, metabolism, insulations i.e. types and a very important topic titled “Ventilation” which I believe to be extremely important. In that subject he talks about fishnet underwear which he refers to as “ventilating underwear.” To follow is the whole subject as he wrote it;
“VENTILATION: Starting with the skin and the need to prevent body moisture from entering the clothing, the requirement is for an air space around the body so the moisture can evaporate and the vapor laden air can then move freely out the neck opening. It will not force itself through the clothing if it is free to leave by an easier method. The many brands of ventilating net underwear are the answer to the problem. They even make an ordinary suit of clothes feel better in winter. The proper type is distinguished by a 3/8 th square mesh or larger, about 1/8 th in thickness and completely open. Smaller holes and “waffle weave” underwear simply do not allow the necessary evaporation to take place. So called “insulated underwear” should not be worn next to the skin except for short periods. It can be used as an effective insulation when worn over ventilating underwear…if great thickness is required. Start out right by keeping body moisture out of your clothing. Wear ventilating net underwear”.
By ventilating evaporative heat loss and conductive heat loss are reduced dramatically.
FISHNET LONG UNDERWEAR
Today Wiggy’s is the only manufacturer of ventilating i.e. fishnet underwear in the USA. It is coincidence that the fishnet fabric I use is knitted with nylon yarns that are about 1/8th inch thick and the holes are 3/8th inch in a circular shape rather than square. Gerry also suggested various thicknesses of insulation that should be worn at different temperatures and during different activities. He was also a firm believer in the use of down as the optimum insulating medium. When I spoke with him about using the information in his booklet when I started Wiggy’s he was delighted that I was going to make his knowledge available to one and all. At that time, 1987, he was still very active and he had a sail boat moored in San Carlos, Mexico which is a town on the Sea of Cortez. He wrote a book about cruising there which he sent a copy of to me and I gave him a couple of my Nautilus bags in exchange. We had sailing in common as well as our business activity; when he told me about the boat I told him about my trip and how the Nautilus bag came to be. It is my belief that if he were active in the outdoor business during the time I have been making Lamilite he would have been a customer for Lamilite. I do not in any way minimize the knowledge that I have acquired from his writings. My own work has been with silicone coated continuous filament fiber trade named Climashield, manufactured by Harvest Consumer Insulations located in Clinton, TN, which when laminated is the primary component of Lamilite.
DOWN
Let us look at “down”. It has been around for less than 100 years as an insulator used in sleeping bags and jackets. Eddie Bauer pioneered its use starting in the 1930’s I believe. The down back then had the same problem it has today: it loses its insulating capability when it gets wet.
That said, down, even when used in ideal dry conditions for a few days at best, does not on an ounce for ounce basis retain heat as well as Lamilite. Down still absorbs moisture, and water repellent treatments are known to break down or wash away.
The Lamilite insulated sleeping bags that I have produced have performed for the temperatures at which I have rated them.
Down also absorbs moisture, and the wetness needn’t come from the outside, because when you are in a down bag the wetness in the down comes from the person in the bag. I know this because of the number of mountaineers I have spoken with who have told me that after about a week in cold dry conditions their bags start showing signs of ice buildup. This also happens with very densely packed polyester bags.
POLYESTER
In 1960 polyester fiber for fiberfill purposes entered the market place as a replacement for “shoddy” in quilted garments. Shoddy was the excess fabric that was left over when garments were cut in factories. Companies known as garnetter’s would be paid to take this fabric waste and then they would chop it up and make a batting out of it. This batting was sold to quilters who in turn sold it to outerwear manufacturers. It did not take very long for polyester to replace the shoddy even though it was more expensive. It was clean light in weight, launder-able and much more efficient as a form of insulation. It was also the original alternative to down. Since I started in the business in 1961 polyester fiberfill existed and it was 40 years later while in conversation with the fiberfill marketing director for DuPont that I learned when polyester fiberfill was first used, about 1960.
The polyester fiberfill that was being made, chopped staple fiber had to go through a quilting process in order for it to be used in manufacturing. Also, the quilting was necessary to hold the fiberfill together when it was laundered. However, with use, wearing a jacket or sleeping in a sleeping bag and stuffing and un-stuffing it as well as laundering then, they would lose their loft; i.e. insulating capabilities. Quilted insulations have an inherent problem in the fact that every stitch line is a cold spot. To keep the fiberfill stabilized the quilting is necessary but that is its downfall. This problem has existed with each and every chopped staple fiberfill used for insulating purposes to this day and will be the same into the future. This also applies to down insulated products, since they must be quilted as well.
Newer polyester fiberfills made to look like down clusters have the same problem that all of these products have: they must be quilted, which means a substantial number of cold spots.
When continuous filament fiberfill entered the market place I was once again present at its beginnings. The year was 1968 and I had been working on laminating fiberfills at that time to eliminate the cold spots that existed due to the quilting process and was unsuccessful because the chopped staple fiberfills available were not suited for the end products I wanted to make. When I experimented with the continuous filament fiber I knew I had found the answer to a product that would revolutionize the manufacture of outerwear as well as sleeping bags. A direct result of eliminating the quilting is an increase in the insulating capability of the product made. By eliminating the quilting the continuous filament fiberfill was allowed to have a uniform loft. The end result of my development work is Lamilite. At the time I was selling insulations to the outerwear industry which included companies that also made sleeping bags. I showed them what I had developed and explained why my lamination process made the insulation work better, and every one of them believed that the general public had no interest in buying sleeping bags that looked like mine, completely un-quilted. They continued to quilt the continuous filament fiberfill that was at the time trademarked Polar Guard. With no quilt stitching there are no cold spots, and the result is a more efficient sleeping bag or garment.
EXPERIENCES
Over the years that I have used the Lamilite for all forms of insulated products; sleeping bags, outerwear, footwear, hand-wear, headwear, dog coats to name a few, incorporating the Lamilite improves the performance of any insulated product. Lamilite has shown some very interesting capabilities that I did not know of when I first started using it, such as its ability to maintain its heat trapping capability even though it was wet. I then noted from a multitude of customers whose bag was wet that a person’s body heat was sufficient to actually drive the moisture out of a sleeping bag over an 8 hour time frame, while they were sleeping, and cause the bag to dry. This action is the most important performance characteristic a sleeping bag can have. One of my customers wrote to me that he put his wet down bag inside of his Wiggy’s over bag and in the morning his down bag was basically dry. Until his account, if I were asked about using a down bag inside of a Wiggy bag I would never have said sure and it will keep the down bag dry. To say I was surprised by this is an understatement. The end result is that even if the Wiggy bag gets wet, it keeps trapping your body heat.
I personally had an experience that demonstrated to me how efficient the Lamilite is when it gets wet. I hunted for a few years in the Fossil Ridge Wilderness which is located basically between Gunnison and Crested Butte Colorado at an elevation of 12500 feet. One year due to a lack of snow to cause the animals to move we went out really looking for them. As a result I was in somewhat unfamiliar territory and got lost. I was out for three days during which a big snowstorm showed up. The mountains make their own weather. I wandered for almost all three days until my guide and friend Rudy Rudibaugh found me. In my wandering I had to cross a number of streams. That was good because I would drink as much water as possible. Now to cross the streams represented a problem as I could not jump them and I did not want to wander looking for a narrower section so I walked right through them. I was wearing the Joe Redington Muk Luks. The snow I was trudging through was as much as 3 to 4 feet deep and the air temperature below zero not taking into consideration wind chill. When Rudy found me we were at about 11000 feet and had to climb to 12500 feet before descending to base camp at 12000 feet. We had one horse, Rudy’s and I was on his back while Rudy led the way. During the climb the temperatures must have gotten down to -30 with wind chill. We had to get into the trees at least six times to get out of the wind. After seven hours we finally arrived at base camp. We finally were met by the cook with a second horse. When I finally got off of the horse and went into the cook’s tent I took off my parka and my Muk Luks. My parka was covered with frost and I was bone dry because I was wearing my fishnet long underwear. All of the moisture my body was generating migrated through all of the materials that were covering my body. Inside of the Muk Luks was water in a liquid state, not ice! I really did not know what to expect. My boots were saturated with water. I thought now that I am safe and alive that I had an incredible experience and an incredible way to find out how well the products I make work. Even though my boots which were foam lined were soaked and my socks were wet my feet were not cold!
Another benefit of having warm feet was a warm head. You have heard the expression wear a hat to keep your feet warm. Wearing a hat will keep your head warm and not your feet if you do not have warm footwear on your feet. During my venture I lost my hood. I did not have any head wear on but frozen hair. My head was never cold in spite of frozen hair and I attribute that to two factors; 1- heat coming out of my neckline and the fact that my feet were never cold during the entire venture. The blood flow to the head is about 15 percent of the blood in the human body. My research showed that at any given time that is the percentage of blood in the brain. Our thigh muscles are the largest muscles in our body and therefore require the largest flow of blood. From the thighs the blood flow is to our feet. If our legs are well insulated as mine were, I was wearing my leg jackets, the blood heated by our thigh muscles is 98.6 degrees and that is what reaches our feet. If our feet are well insulated the blood flowing back to our heart will not have cooled down very much if at all. The end result is that the blood flow to our head is very constant with that of the rest of our body. It takes approximately one minute for the blood to make one circulation in the body in a rested state. Also when we are active the flow of blood through our body is more rapid than when we are at rest so it gets very little chance to cool if we are well insulated, as I was. The leg jackets that I was wearing gave me the added leg protection. The same would be true if you are wearing mittens versus gloves, keeping your hands warm again means the blood flow returning to the heart will be much warmer. The steps that you take to keep your extremities warm means that the rest of your body stays warmer and your body works easier to keep itself warm.