Down Sleeping Bag

Warmth by loft, weight by the gram

A down sleeping bag is filled with the fine clusters found beneath the outer feathers of geese and ducks. Those clusters lock together into a springy structure full of still air, and still air is what insulates. The bags here run from ultralight waterproof shelled models to extreme cold and extra large winter patterns, in both goose and duck fill. How they perform, and how they should be treated, follows from one fact: the warmth lives in the loft, not in the weight of filling.

Is goose down better than duck down?

They behave the same way, and the difference is cluster size rather than species. Larger clusters trap more air for a given weight, so a bag that lofts higher is warmer for its mass. Geese are bigger birds, so clusters tend to be larger, but a high grade duck fill will beat a low grade goose fill. Judge a bag by how much it puffs up when shaken out rather than by the bird named on the label.

Why does damp matter so much?

Wet clusters clump together, the structure collapses, and a flattened bag holds almost no air. The bag has not failed; it has lost the shape that does the work, and it dries slowly. Two habits prevent it. Air the bag each morning before it goes back in the sack, since a night of breathing leaves moisture in the filling. Where condensation drips from a tent wall, or the plan involves no tent, a bivy bag over the top keeps moisture off the shell.

What should you look at on the product page?

• Baffle construction: internal walls between the outer and inner fabric hold the down in place. Stitching the two layers straight through is lighter but leaves cold lines along every seam.
• Shell fabric: a tightly woven or coated outer resists the damp that down cannot cope with, and stops clusters working their way out.
• Draught collar: a filled tube around the shoulders traps the warm air that otherwise escapes at the neck every time the sleeper turns.
• Packed volume: down compresses far smaller than synthetic filling, which is the reason to choose it and the number worth comparing.

How should a down bag be stored and washed?

Store it loose and dry, hung up or in a large breathable sack. Months squashed in a compression sack take the spring out of the clusters permanently. Wash it rarely, in a large machine, with a cleaner made for down rather than ordinary detergent, which strips the oils that let clusters spring back. Drying takes hours on low heat, with a few tennis balls to break up the clumps. Sleeping in a sleeping bag liner pushes that wash years further apart.

What goes underneath it?

Something with its own structure, because body weight flattens the down beneath the sleeper to nothing. That flattened underside is why a quilt leaves it out and relies on the mat instead. A foam sleeping mat puts trapped air between the bag and the cold floor. For winter nights and for side sleepers, a self inflating mattress adds thickness as well as insulation. A capable bag with no mat wastes most of what the filling can do.