Store a sleeping bag dry, uncompressed and somewhere the temperature and humidity do not swing — that is nearly the whole answer, and the stuff sack it travels in is where bags go to die. The maker’s own care instructions govern the details, and most of them say a version of this.
Why compression is the thing to avoid
A bag keeps you warm by holding dead air, and it holds that air by lofting. The EN 13537 and ISO 23537 comfort and limit figures a maker publishes are laboratory values measured on a heated mannequin, and they are measured on a bag at full loft. A bag that has lost loft is no longer the bag those figures describe. That is not a warning about temperature; it is a statement about what the number refers to.
Months of sustained compression is what tires insulation. Down clusters lose some of their ability to spring back; synthetic fibres take a set and do not fully recover. The stuff sack is designed for a few days in a rucksack, not for the winter.
What to store it in
Most bags are supplied with a second, much larger bag — a cotton or mesh storage sack — and it exists for exactly this. Where one was not supplied, a pillowcase, a laundry bag or a large mesh sack does the same job.
Hanging works too, and takes less floor space than a box. Hang it by the foot end loops if it has them, or over a wide rail rather than a thin wire hanger that concentrates load in one place.
What not to use: the stuff sack, a compression sack, a vacuum bag, or a sealed plastic box. The first three keep it compressed; the last keeps any residual moisture in with it.
Dry, and dry through
Put it away dry, which means drier than it feels. A bag that comes home from a damp weekend has moisture through the fill even where the shell feels fine, and moisture in storage is what produces the smell people mistake for a manufacturing fault.
Air it opened out for a day or two before it goes away — inside out for part of that, since the inner surface is where body moisture went. Somewhere with moving air rather than direct sun, because prolonged ultraviolet is hard on shell fabrics.
Then choose the place. A cupboard indoors is better than a loft that bakes in summer and freezes in winter, and much better than a garage or a cellar that cycles damp. Off the floor, away from radiators.
Cleaning before it goes away
Whether to wash before storage is a judgement, and the care label and the maker’s instructions decide how. Washing is mechanically hard on insulation and on baffle stitching, so the usual approach is to reduce the need for it: a liner takes body oils and washes as ordinary laundry, and sleeping in clean base layers does the same.
If the bag has had a hard season and airing has not restored the loft, that is when a wash is worth it — and a bag washed for storage must be completely dry before it is put away, with no clumps left anywhere in the fill.
The rest of the kit, while you are there
Tents want the same treatment for a different reason: a fly put away damp grows mould that stains permanently and attacks coatings, so pitch or hang it until it is dry through and store it loosely rather than crammed.
Inflatable sleeping mats are commonly stored unrolled with the valve open, so the inside dries and the foam or baffles are not held compressed. Check what your maker states, because self-inflating and air-only constructions differ.
Gas canisters, batteries and filter cartridges all have their own storage instructions from their makers — freezing in particular is what ends many filter cartridges early. Those instructions come with the product, and they are the ones to follow.
The manufacturer's own instructions come first, and this page does not stand in for them. Every weight, packed length, hydrostatic head, denier, micron rating, lumen figure and temperature on this page is reported from the manufacturer's own documentation, with its unit written as published, and named as such — none of it is measured here. A weight is reported as the maker counts it, and is never restated as another kind of weight, because the two are not the same figure.
What people ask before buying
Does it matter if a synthetic bag is stored compressed?
It matters for both fills, and arguably more for synthetic. Down clusters recover from compression better than synthetic fibres do, and a synthetic bag left crushed for months loses loft it does not fully get back. Store either one loose and the question goes away.
Can I store a sleeping bag in a vacuum bag to save space?
That is the opposite of what makers ask for. A vacuum bag is sustained maximum compression, which is the condition storage is meant to avoid. Where space is the constraint, a large mesh sack hung in a wardrobe takes less floor area than a box and keeps the bag lofted.
Last reviewed 6 September 2026