Short answer: Buy for the comfort rating, not the limit rating. A bag described as comfortable to a given temperature will keep an average sleeper warm at that temperature; the lower “limit” figure assumes you are a warm sleeper in a full base layer. For winter, choose down if you are carrying the bag and synthetic if you expect it to get damp – and choose a mummy shape if you want maximum warmth for the weight.
What do the temperature ratings on a sleeping bag mean?
Short answer: There are usually three: comfort, limit and extreme. Comfort is the temperature an average woman sleeps comfortably at; limit is the boundary for an average man; extreme is a survival figure and not a target. Plan around comfort.
| Shape | Warmth for the weight | Best for |
|---|---|---|
| Mummy | Highest | Cold weather, backpacking, minimum bulk |
| Envelope / rectangular | Lower | Warmer months, car camping, more room to move |
| Double / wide | Moderate | Two people, or one person who wants space |
Down or synthetic – which is better for winter?
Short answer: Down is warmer for its weight and packs smaller, but loses its insulation when wet. Synthetic keeps some warmth even when damp and dries faster. If you are backpacking in dry cold, take down; if you expect condensation or rain, take synthetic.
How do I look after a sleeping bag?
Short answer: Store it loose, not compressed – a bag that lives in its stuff sack loses loft over a season. Air it after every trip, wash it rarely and gently, and dry it fully before storing. Loft is the insulation, so anything that flattens the fill reduces warmth.
Should I buy a bag rated colder than I think I need?
Short answer: One step colder is sensible; three steps colder is wasted weight and money. Temperature ratings assume a full sleeping pad and a dry base layer, and most people who sleep cold are losing heat downward rather than upwards.
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