Insulation - Down
Down provides the warmest available clothing for its weight and is much used for high altitude climbing. It compacts very well too, thus making it easy to stow in a rucksack.
Its drawbacks are that the best quality is expensive and that down is vulnerable to moisture and is thus not suitable for wet conditions. If it gets wet, it loses virtually all it's thermal properties and needs careful drying out or it will be ruined (to dry out down clothing, tumble dry at a low heat setting with an old training shoe in the dryer to knock the down around and fluff it up a bit).
The best quality down available is goose down which comes mainly from Eastern Europe and China. The higher fill power, the better the loft (or air trapping ability) of the down. However, due to a difference in the way fill power is measured on either side of the Atlantic, American down clothing and sleeping bags show higher fill powers than European ones. An American fill power of 850 is equivalent to a UK fill power of 750, and this is about the highest available.
All down used in the Rab clothing we stock is from Eastern Europe and is fully cleaned before use. This gets rid of the bird dandruff that may not be removed from cheaper products and which can cause allergic reactions in some people. Rab down is not "live plucked" - a byproduct of the food industry, it is taken from dead birds, a slightly more humane method.
8000m+ Down: Down clothing designed to cope with moving very slowly and remaining stationary at high altitudes and/or temperatures of -30ºC and below.
7000m Down: Down Clothing designed to cope with moving very slowly and remaining stationary at high altitudes and/or temperatures of -20ºC to -30ºC.
6000m/Alpine Down: Down clothing designed to cope with moving slowly and remaining stationary at altitude and/or temperatures of 0ºC to -20ºC depending on fill quantity.
Low Level Down: Down clothing for day to day wear and back up warmth.
High Altitude Down Accessories: Down mitts and booties.