There's no such thing
as bad weather - only the wrong clothes.
The shell layer takes the direct battering
from the elements. It should be at least windproof and preferably
waterproof too (but see below in very cold temperatures).
Antarctica is the windiest place on earth, so don't
skimp on this or imagine that you can get by with an outer
garment that is "pretty windproof".
Antarctica does proper wind. Proper
biting - gets through every nook and cranny - straight to
the bones - wind.
Some garments such as duvet
style puffa jackets have a wind-proof outer nylon layer
but are not waterproof. This has the advantage of making
the garment softer, pliable and comfortable and of also
reducing the cost. Water-resistant or water-repellent are
fine if you will not use the garment in extended wet conditions
or and will have the opportunity to dry it out between uses.
In cold conditions, waterproof is not necessary as there's
not a lot of liquid water about!
500 / 600 / 700 fill down? The
number is a measure of "fill power". This
measures the amount of space taken up by one ounce of down.
Take one ounce of down, compress it and then release it
- on release the down will expand and fill up a certain
volume. The volume it occupies is measured in cubic inches
and is the down's "fill power". The higher
the number, the higher the quality of the down -
As well as down quality, the fill power
is what gives the down its insulating properties. The more
the fill power, the warmer the jacket - generally.