Education

How to Sell: The Science of Warmth

No doubt, most of us are at least familiar with the story of Goldilocks and the Three Bears. After trial and error, she finds a porridge that is neither too hot nor too cold, but just right. Ditto for the comfy bed. Yet, while the outdoor industry has reams of knowledge to share on layering, numerous insulation types, and even temperature ratings for sleeping bags, more often than not, helping a customer find the right combination of garments or the right sleeping bag to stay warm comes down to trial and error. But it doesn't have to. There is a science to keeping warm.


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No doubt, most of us are at least familiar with the story of Goldilocks and the Three Bears. After trial and error, she finds a porridge that is neither too hot nor too cold, but just right. Ditto for the comfy bed. Yet, while the outdoor industry has reams of knowledge to share on layering, numerous insulation types, and even temperature ratings for sleeping bags, more often than not, helping a customer find the right combination of garments or the right sleeping bag to stay warm comes down to trial and error. But it doesn’t have to.

There is a science to keeping warm.

Let’s start with a bit of Biology 101
When the temperatures dip and the body is trying to stay warm, heat is conserved first by constriction of blood vessels near the body surface. When that fails to work sufficiently, the body triggers shivering (essentially rapid muscle contractions) to increase metabolism. Studies have shown that shivering can result in a five-times increase in metabolism. But even with all the body’s best efforts, when it is naked, it cannot sufficiently increase metabolic rate to replace heat loss to the environment once the temperature dips below about 40 degrees F or 4 degrees C. While the body also generates goose bumps (something known in scientific circles as piloerection), it’s really an attempt to raise the body hairs which doesn’t work too well since most humans are quite hairless.

Our only alternative is to insulate artificially with clothing, sleeping bags and more.

How does a person lose heat?
People lose heat four ways:

  1. ConductionMeaning surface-to-surface contact, conduction allows us lose heat through the soles of the feet or our body when lying or sitting on colder ground, for example.
  2. Convection — Convection is heat lost by air circulating around our body or via respiration when we breathe.
  3. Evaporation — Evaporation of moisture from our skin chills our body, which is great when we are too warm, but not so good when we are trying to stay warm.
  4. Radiation — Although a very small part of heat loss, the body does lose heat via radiation of that heat outward.

The body is the engine and only means of generating heat
When you strip away all the technical data and discussion of variable metabolisms, etc., you arrive right at the heart of staying warm. The body will feel warm only if it is producing heat at a level that is equal to or greater than the heat it is losing to the environment around it.

Layers of clothing, sleeping bag insulation or any other artificial means of retaining heat around the body is only as good as the heat being generated by that body. And here are where the variables come into play — psychological, physiological and environmental.

So what is a person to do?
Insulate. Layer up. Dress for success. And your job as a salesperson is to help your customer understand what the best clothing system is (combinations of base layers, middle layers, outer layers and shells) and best sleeping bag system (bag, sleeping pad, maybe a bivvy sack, certainly a tent) that will help them stay comfortable. And by comfortable we mean, neither too hot, nor too cold, but just right.

What the heck is a CLO?
Your customers may ask you about CLO, and even some of your reps and training manuals may reference CLO or CLO value. Developed in 1941, it was the first real attempt to explain the insulation value of clothing so people would know how much clothing they might need to stay warmer or cooler in a given temperature environment. A CLO value of 1 is defined as the amount of clothing required by a resting human (in other words, sitting, lying down or standing, but not moving) to be comfortable at a room temperature of 21 degrees C, or approximately 71 degrees F. That single value of CLO is equivalent to a typical business suit worn by a man — shirt, undershirt, trousers and suit jacket. The higher the CLO number, the more insulating value is provided.

Yeah, but who hikes in a business suit?
Not many folks. But it is a good point of reference. Think of it like this: If something has a CLO value of 2, it means it provides the same amount of insulation as two suits. All garments and even sleeping bags carry a CLO value. As a point of comparison, the Department of Performance Textiles at Leeds University in the United Kingdom developed a comfort model to relate the thermal resistance of sleeping bags to temperature ratings. The study found that a CLO value of 2.5 was needed to keep a sleeping person comfortable at an air temperature of 59 degrees F, or 15 degrees C. A CLO value of 4 was required for comfort at 48.2 degrees F, or 9 degrees C. Thirty-two degrees F, or 0 degrees C, you’d need a CLO value of 6.

Just as there is a CLO value for sleeping bag insulation, there is a CLO value for most every garment possible. And, CLO values are cumulative, meaning as you help your customer layer, the sum of the CLO values of each component in the layering system will approximate how warm a person might expect to be. The following represents average CLO values for various articles of clothing, according to the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE): T-shirt, .09; Long Underwear Top, .35; Long Underwear Bottoms, .35; Heavy Long Sleeve Shirt, .29; Basic Sweater, .10; Socks, .08; and Long Pants, .32.

So, a person dressed in socks, long underwear, sweater and long pants would have a clothing system with a CLO value of 1.2.

Shedding the elements
However, no matter how many layers you dress your customer in, they’re not going to stay warm or comfortable if the wind if howling through the fabric weaves or freezing rain is pounding down so hard it soaks through every possible fiber. And this is where it becomes important for you, as a salesperson, to understand what garments do what in your store’s arsenal. Some are more air permeable, some are less. Some are more waterproof, but less breathable. Others are more breathable, but less waterproof. Some shed light mist, but stop a wind blast dead. Others let a little wind through, but still shed misty air.

At all times, think about what your customer is doing, and how you can best help them manage the heat-generating engine. Are they looking to stay warm while running? Likely they’ll need less layers and more streamlined ones than a person seeking to stay warm while simply walking. You want to keep the engine as dry as possible when it is cold so it will not chill. You also want to be sure that you are not piling so many layers on that the engine overheats.

By applying a bit of science to the dressing equation, you’ll better serve your customers, and yourself.

For more on sleeping comfort, we’d recommend downloading the Sleep Well PDF produced by Mammut by clicking here.

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