PeakLite Goose Down Jacket

Fill power measures how fluffy the down is — how much air it traps. Trapped air is what keeps you warm, so fluffier down gives you more warmth for less weight.
700 means one ounce of this down fluffs up to fill 700 cubic inches. Most down jackets fall between 550 and 800. 900 is about the best down there is, and it is usually saved for expedition and ultralight gear where every gram matters.
Fill power tells you how good the down is, not how warm the jacket is. For that you also need to know how much down is in there — that is the fill weight.

Down and feathers are not the same thing. Down is the soft, fluffy cluster with no quill in it, and that is the part that traps air. Feathers have a stiff shaft, add weight, and hold very little air.
90% — often written as 90/10 — means nine-tenths of the fill is down cluster. Most down jackets fall somewhere between 75/25 and 90/10. The remaining tenth is mostly broken-off down fibers and small feathers rather than whole ones, and the split is measured by independent labs such as IDFL.
A high down content means more of the jacket's weight is actually working for you.

Fill weight is how many grams of down are actually inside the jacket. Fill power is about the quality of the down; fill weight is about the quantity.
Light packable jackets usually carry 60 to 120 g. Everyday winter jackets sit around 150 to 250 g. Expedition parkas go past 300 g. Bigger sizes hold more down, so we list size L as our reference — smaller sizes have a little less, larger sizes a little more.
Read it alongside fill power.

Comfort is the temperature where most people stay warm standing still, with a normal layer underneath. Limit is where you start to feel cold but are still protected as long as you keep moving.
14°F is a typical clear, still winter morning across most of the northern US. −4°F is the kind of cold that arrives in a cold snap or at elevation. Wind, how hard you are working, and what you have on underneath will move both numbers in either direction.
This is a Sounor rating, not a certified result. There are standards for measuring a garment's insulation, but none that turn it into a temperature rating — every jacket rating on the market is the maker's own, ours included. We publish ours anyway, and say plainly what it is, because a number you can read for what it is beats no number at all.