For our expeditions to Mount Aconcagua, one of the articles on the equipment list is a down jacket with hood.
It is important to have a jacket rated for at least -15 ° C / 5 F and have a high ‘fill power’. ‘Fill power’ is a measure of the amount of ‘loft’ of a down product and it is directly related to the insulation value and the quality of the down. The higher the ‘fill power’, the greater amount of air is trapped, therefore providing a higher insulation capacity.
Down is the best natural insulator. It is extracted from the chest and under the wings of a goose without killing or harming the animal. It is not a feather as the regular feather has a shank and a 2-dimensional planar structure. Instead, down has no shank and it seems that from a point thousands of filaments emerge surrounding it.
Down is washed and cleaned with chemical products and then separated into different categories using an air pressure device. The air currents place the best down in a higher compartment, separating this from lower quality down.
Its high insulation is due to its three-dimensional structure and its capacity to swell, each duvet snowflake stores more air than any synthetic snowflake. Hairy filaments overlap and form a protective layer that retains the heat and insulates from the cold. Because of its elasticity the jacket can be compressed for transport, being much more compact and lighter than a synthetic one (Thinsulate or Primaloft).
The down jacket is generally used in Base Camp and high camps, when we are resting and during the final ascent on summit day.
During the approach and ascents to the high camps we use several layers that allow us to keep our body warm. Layering provides the most freedom to regulate temperature without carry excess amounts of clothing. As a base layer, we would recommend a merino or synthetic t-shirt with additional layers comprising of a fleece, windproof jacket and a windproof, waterproof and breathable Gore-Tex jacket large enough to cover all layers for summit day. This system allows us to regulate body temperature by opening or closing zips as well as removing or adding more layers.