Fill weight at a glance
- Given in
- Grams or ounces
- Multiply by
- Fill power, for total loft
- Often
- Not published at all
Why fill weight and fill power go together
Fill power describes the quality of the down. Fill weight describes the quantity. Total loft, which is what actually keeps you warm, comes from multiplying the two, so knowing one without the other tells you very little.
Where brands cut cost quietly
This is where a lot of quiet cost-cutting happens. Two bags can both advertise 800 fill power and carry temperature ratings ten degrees apart, because one has considerably more down in it. Brands that publish both numbers are giving you enough to compare properly, and brands that publish only fill power are usually not the ones with a generous fill weight.
Why a very light bag can sleep cold
It also explains a specific disappointment. A very light bag with a high fill power and an optimistic rating often has a thin fill weight, and it will feel cold at the temperature on the label. When a bag looks suspiciously light for its rating, the missing down is the reason.
What this means when you're choosing
- Both numbers published together, which is the sign of a brand happy to be compared
- Total bag weight against fill weight, which tells you how much is shell and zip
- Whether the rating is an EN/ISO limit or comfort figure before you judge the fill
The common mistake
Comparing two bags on fill power alone
Fill power is quality and fill weight is quantity, and warmth needs both. Two bags at 800 fill can be ten degrees apart because one has considerably more down in it. If a brand publishes only fill power, that is usually the tell.
Common questions
Why don't all brands publish fill weight?
Because it's the number that exposes a thin bag. Fill power sounds impressive on its own, and a maker cutting cost by putting less down in a bag has no reason to advertise it.
How do I compare two bags if only one lists fill weight?
Fall back on the EN or ISO rating, which is measured on the finished bag and reflects however much down is in it. Total weight is a useful sanity check too: a bag much lighter than its rated peers is usually lighter for a reason.
Where this is defined
- Testing regulations for down and feather, International Down and Feather Bureau