Friday, 28 December 2012

Keeping Warm Part 2: Insulation

Staying Warm 99In my summary post on how to keep warm, I mentioned how critical is was to have proper insulator thickness. In this post, I will look at this issue in more detail.

Insulator Thickness
To understand how the thickness of an insulator helps you, you should be passingly familiar with Fourier's Law, which is q = k A dT/ s . However, if you are math-phobic, you can skip this part and go to the next paragraph where I will give you a layman's description. In the equation:

q = the heat transferred
A = heat transfer area
k = thermal conductivity of the material
dT = temperature difference across the material
s = material thickness

The amount of heat transferred, q, is what will make you feel cooler. The higher the "q", the cooler you will feel.

Here is the non-math interpretation:
  1. The amount of heat you will lose on a cold day is directly proportional to your body area, and the exposed surface of your body. The more surface area you have exposed (as in bare skin), the faster you will lose heat and feel cold. To warm up, you need to cover up!
  2. The colder it is out, the faster you will lose heat and feel cold.
  3. What you wear will make a difference. If you wear a trendy, latest fashion jacket made from woven metal fibres, you are going to lose heat a lot faster than if you wear a regular, wool sweater.
  4. The thicker the clothes you wear, the less heat you will lose and the warmer you will feel. Double up to warm up!

What can you control? Well, you can easily control the thickness of what you are wearing! You can easily put on another sweater or pull on long underwear. You can put on a thin pair of glove liners inside your regular gloves or mittens. You can pull a hood up over your toque (which is a Canadian word for warm hat).

In some limited cases, such as the use of mittens instead of gloves, you can control the surface area, but the rest of the factors are outside of your control.

You might think that changing your insulator makes a big difference, but when it comes to just looking at thickness, as long as your insulation layer is really an insulator (think sweater) and not a conductor (think aluminium foil), it generally doesn't. For those of you interested, the Engineering Tool Box has a list of some materials and their thermal properties here. Where the type of insulation you choose will play a factor is when it comes to wetness (water conducts heat much more efficiently than cotton, wool, polyester, or polypropylene), which I will look at in a few minutes.

So how thick is good enough?

That depends upon your personal situation; How cold do you feel? How much heat are you putting out, either through your basal metabolic rate or through your activity?

The more heat you put out, the less insulation you will need. The less heat you put out, the more insulation you will need.

Cross-country ski racers wear very little insulation because they generate enormous amounts of heat while racing. However, when they stop, they need to add insulation pretty quickly. They usually have a bag of clothes at the finish line so that they add clothes or switch clothes just after their race.

Final Push

Cross-country ski officials, the folks who run the race, tend to generate heat in bursts. For short periods of frantic activity, we need little insulation. For example, this is me on the left. Len and I are out manually grooming a corner and I am down to one thin underlayer plus the required uniform shirt (note the NEOS on my feet for better foot insulation in the snow).


For the longer periods of time when we are mostly standing around, we need more insulation and we layer up, with lots of wind block as well (note on the second photo the hoods up to block wind and protect the head and neck as well as the pads to get more insulation thickness between the feet and the snow)

The Loneliness of the Long Distance Event Offical

Staying Warm 98

When I am out taking photographs, I generate very little heat, so I need a lot more insulation than I do for my other activities.

To stay warm, you need to develop a feeling for how much insulation you need for doing various activities, no matter if it is shoveling snow, taking photographs in the city, taking photographs in the mountains, or running along a park trail.

You also need to pay attention to the different parts of your body, because some areas may require more insulator thickness than others. I find the areas where there is a lot of blood flow near the surface requires more insulation. These are my head, my neck, my hands, my wrists, my groin (where the femoral artery is) and my trunk. I need to wear light gloves starting at 5 C. Other areas require less insulation. I wear shorts (while running) until it is 0 C. I only need to cover my face (while running or skiing) when it goes below -15 C.

Changing activity means you need to manage your insulation, which you can do by wearing layers. Rather than wear one big, thick piece of clothing, you can "layer" your insulation by wearing more, but thinner, clothing.

During the oil crisis of the 1970's, we lived in a big, drafty house heated by an oil-fired furnace pumping hot water through radiators. Naturally, we turned down the thermostat to conserve our oil. Whenever I complained about being cold, my mother would admonish me to "go put on a sweater!" A great example of layering!

You can take an extra sweater with you when you go out, if you are not sure if you will be warm enough on your trunk. Then if you are cold, put on your extra sweater for an additional layer of insulation.

You can also start out by wearing two or more layers and removing layers as you heat up. If you get cold, put a layer back on. It is much better to remove a layer when you are warm, than to sweat into the layer and get it wet.

For example, if I am carrying my camera gear in my backpack and I'm meeting someone for a coffee before we shoot, I will immediately start to "de-layer" as soon as I go inside. I do this because I know I have been generating lots of heat carrying my gear, possibly even getting my insulation damp from sweat. De-layering not only allows me to not overheat and to not sweat into my insulation while inside, but also to let my layers dry more quickly than if I had not de-layered. If I didn't do this, I would be nice and toasty on the way to the meet-up, but as soon as I stepped outside for the shoot, I would start to freeze because my layers would now be wet (or even only damp). What the frack? I was warm on the way down!

If you only have one layer, then your options to regulate your heat loss is very limited and you are much more likely to sweat into it than not.

Here is an example. You can see I am wearing three layers in this photo: a turtleneck poly shirt, a poly fleece on top of the turtleneck, and then an insulated jacket. I could easily add more layers by wearing a thin poly undershirt, and/or a thicker fleece sweater between the top shirt and the jacket.

Staying Warm 97

When I talk about layers and insulation, I am not just talking about sweaters or jackets. The "thickness" and "layer" principles apply to your hands, feet, neck, head, and every other part of your body. I have already mentioned that I often wear thin "liners" or kids gloves under my regular gloves, but I also will wear a really thin hat under my normal hat, or, wear a hat and if I am cold, pull up my hoodie over it. Pulling up a hood also helps insulate your neck.

One great little piece of gear is a Buff. They are thin pieces of insulation that can be used as an extra layer:

On your neck:
Staying Warm 26

Up over your face:
Staying Warm 25

Around your neck and head:
Staying Warm 24

Around your neck and head under a toque:
Staying Warm 23

Worth a special mention, I think, is wearing gloves just as you start to get cold hands. I find many people complain about cold hands between 5 C and 0 C because they think it is too warm to wear their big, heavy winter gloves. For many people, those thin glove liners are just the right thickness to wear in this temperature range and they roll up nicely into your pocket so you don't forget to bring them along!

So don't forget to apply this thinking to all parts of your body where you get cold.

I mentioned surface area above, and in particular mittens versus gloves. Mittens are much warmer than gloves because they have a smaller surface area that is exposed to the cold. The trouble with mittens is that you lose the dexterity of your fingers while wearing them.

However, mittens work especially well for me when I wear the glove liners I just mentioned. By wearing them under my mittens, I can whip my mittens off, do some fine finger work (taking pictures, waxing skis, etc.), and then pull them back on without getting too cold on my fingers.

Glove liners or thin knit gloves:
Staying Warm 33

Mittens on over the glover liners:
Staying Warm 32

The final product (note the draft strap on the wrist):
Staying Warm 28

A special comment for photographers: depending on how cold it is and how long I am shooting, I may upgrade my glove liners to gardening gloves or cross-country ski gloves. They have more insulation and typically are more "grippy" which helps when fiddling with camera parts, yet are still thin enough to fit inside my large mittens for when I am not actually shooting.

You need to watch out for compression of your layers because compressing an insulator reduces its ability to keep you warm. Compressing a layer reduces its thickness, meaning more heat will "leak" out. Socks in particular are prone to compression on the underside of your foot, so you may need thicker socks than you think. Be very careful not to go with too thick a layer, though. You may restrict blood flow, and restricting blood flow will cause all sorts of problems!

If you cannot put on another sock, then take a look at your shoes or boots. Many shoes have thin soles and you will lose heat through them fairly quickly. If you have to wear dress shoes, try putting on overshoes, like the NEOS I mentioned in an above photo. I use NEOS over my hiking boots when I am standing around on the snow. I find that extra layer of insulation is just enough to keep my feet nice and warm, and I can easily de-layer if I go inside. I also use them when I am heading to a formal function and wearing my dress shoes. They keep my feet warm and toasty and it is very easy to pull them off when I get to where I am going.

Wear is another issue you need to watch out for. Gloves and socks are particularly prone to wear and you can end up feeling surprisingly colder than you thought you would feel.

So in summary: the thicker the insulator, the warmer you will be. You just need to remember to cover-up everywhere, and not just your trunk.

The complete Keeping Warm series is here:

Keeping Warm: Summary
Keeping Warm: Insulation Thickness
Keeping Warm: Dryness
Keeping Warm: Wind

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