|STAYING WARM IN INSULATED CLOTHING|
Owning a down parka is a fashion statement these days. For outdoor lovers or explorers, however, the functionality of an insulated garment makes it more than a fashion trend. For 8000M climbers or Polar Explorers the insulation and design or a parka can be the difference between life and death. One-piece insulated clothing has a higher warmth-to-weight ratio than a layering system and can be less restrictive for active use.
Read more about Insulation and Fabrics.
A working knowledge of thermodynamics will help you understand how insulated clothes work, and which ones are best for you.
You loose body heat in four ways:
- Conduction - through direct contact with a colder surface
- Convection - through air currents that carry heat away
- Radiation - your body gives off infra-red radiation, or heat waves
- Evaporation - through evaporation of moisture (sweat or wind dried precipatation)
All insulation works in the same way. A web of fibres traps a layer of still air, reducing heat loss due to conduction, convection, and radiation. The warmth of a given insulating material is a function of its thickness, or loft (thicker insulation traps more air), and the surface area of the fibres present (more surface area means the insulation is better at holding air still), the shell material, and the way the garment is sewn.
The way an insulated garment is sewn can dramatically affect its warmth. There are seven basic construction methods used in down garments:
- Stitch-Through or Quilted - the most common and least expensive method. The shell and liner are sewn together to hold the insulation in place. Although this method creates cold spots along the stitch lines, it is sufficient for day to day conditions.
- Box Wall - box walled channels allow the filling to achieve a deep loft right to the edges of the channels, thereby reducing cold spots. Suitable for extreme cold conditions.
- Double Construction - 2 insulation layers, combining natural and synthetic fibres. Extemely warm with the synthetic fibres providing protection against heat loss through build up of moisture. Suitable for extreme cold conditions where the added weight of this style of construction is not a problem.
- Double Stitch-Through - two quilted layers are arranged so the stitch lines are offset. This eliminated cold spots, but is heavy and bulky. Also relatively inexpensive.
- Trapezoid - sewn channels hold the down in place while eliminating cold spots. Much less bulk than offset quilting. Although expensive, this method provides the ultimate warmth without excess weight.
- Double Box Wall - possibly the warmest construction method with no cold spots. Very expensive and also heavy.
- Triple-layer - a good compromise--a free-floating layer of waterproofed (Gore-Tex) fabric is draped over Double Stitch-Through tubes. This method also increases wind resistance, and reduces heat loss.