Warmth?
Dinkleberg trying to keep warm at Dragonfly Creek
Thermal Conductivity of a Down Jacket
Keeping warm is a major key to success in Ice Climbing. This can be complicated because during climbing, the body is much warmer than it is while belaying or taking breaks. This means that it is very important to wear many layers that can be easily added or taken off. It can be extremely dangerous on long climbs to get too cold; it can lead to rash decision making and dangerous circumstances. One of the most vital layers is the down jacket. It is very compressible so it is easy to carry, and extremely warm.
Layering up on the ridge after a climb at peak 9400.
Understanding the thermal diffusion of different qualities and thickness of down can help a lot to determine which type of jacket is best for the current conditions. A good scenario to look at is, how efficient will a 750 fill down jacket be when it is -20 degrees Celsius, assuming the surface area is 1.5 m^2 and the thickness is 3.5 cm. We also know that the thermal conductivity, K, of 750 fill down is .025 J/(mKs) and the average skin temperature is 36 degrees Celsius.
This thermal conductivity is relatively good compared to other jackets, and would be an excellent choice for a chilly negative twenty degree day. It is also important to note that this represents the amount of heat the jacket lets leave the body, not the amount of cold it keeps out.