Gear

Down sleeping bag

Sleeping bags with a down fill. Lighter and pack smaller than synthetic — but vulnerable to damp, more expensive, and call for an ethical assessment of down production.

Down bags are lighter than synthetic bags relative to their warmth, and they usually pack down far smaller. Those are the main reasons down is popular on long and demanding trips where weight and space matter.

What do the various markings mean?

On down sleeping bags you typically see four product details that tell you something about the quality:

Type of down. Duck down or goose down — or a blend. Goose down is the warmest and most expensive; duck down is the reverse. For most trips the difference is small in practice.

Down/feather ratio. The fill is usually a blend. Feathers are cheaper but have a lower insulation value. A good sleeping bag has at least 80% down. If it says ‘90/10’, that means 90 g of down per 100 g of fill.

CUIN (fill power). The unit of measurement for the loft of the down. Higher = better insulation per gram. 550–750 CUIN counts as very good quality, anything over 750 as excellent.

Certification. Down production has a dark history of live plucking and force-feeding. Certifications such as RDS (Responsible Down Standard) guarantee that the down comes from birds in meat production — a by-product of animals already slaughtered — and not from poor animal welfare. Choose certified down.

Rule of thumb

An inexpensive down bag often has duck down, a high feather ratio, a low CUIN and is rarely certified. An expensive down bag sits at the other end: goose down or a good blend, ≥90/10, a high CUIN, certified.

For practical use: go by the stated comfort temperature set against the weight. That tells you more than the details on a spec sheet.

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