Temperature Ratings Explained

Sleeping bags are rated using the European EN/ISO standard with three temperatures:

  • Comfort rating: The temperature at which a cold sleeper (typically a woman) will sleep comfortably. Use this as your main guide.
  • Lower limit rating: The temperature a warm sleeper (typically a man) will sleep comfortably.
  • Extreme rating: The minimum temperature at which survival (not comfort) is possible. Do not use this for trip planning.

Choose a bag rated 5–10°C lower than the coldest temperature you expect. It is easier to sleep with a bag unzipped than to warm up in an insufficient bag.

Down vs Synthetic Fill

  • Down (duck or goose): Lighter, compresses smaller, more durable long-term. Much better warmth-to-weight ratio. More expensive. Loses all insulating ability when wet and takes a very long time to dry. Best for dry conditions and ultralight backpacking.
  • Synthetic (polyester fibres): Retains some warmth when wet and dries faster. Heavier and bulkier than equivalent-warmth down. Cheaper. Best for wet conditions (rainforests, kayaking, coastal camping) or as a budget option.

Shape

  • Mummy: Tapers from shoulders to feet. Minimal dead air space to heat. Warmest for weight. Less comfortable for those who move a lot in their sleep or prefer room to move.
  • Rectangular: Most room inside. Less efficient thermally. Good for warm-weather camping, car camping, and those who find mummy bags claustrophobic.
  • Semi-rectangular: Compromise — more room than mummy, warmer than rectangular.
  1. 1

    Match the rating to your use case

    Weekend camping in summer in Australia: a +10°C to +5°C bag is usually sufficient. Alpine or mountain camping: 0°C or below. Multi-season bag for year-round use: -5°C to 0°C with a liner for warm nights.

  2. 2

    Consider your sleeping system

    A sleeping bag works with your sleeping mat (pad) — the mat insulates from cold ground which the bag cannot do on its own. A high-quality mat significantly extends the effective temperature range of your bag.

Down fill power explainedFill power (e.g. 600fp, 800fp, 900fp) measures the loft of one ounce of down. Higher fill power = lighter and more compressible for the same warmth. A 900fp bag packs much smaller than a 600fp bag at the same temperature rating. Worth paying for if weight and pack size matter.

Frequently Asked Questions

Machine wash on a gentle cool cycle with a front-loader (top-loaders with agitators can damage the baffles). Use a specific down wash (Nikwax Down Wash) or a gentle detergent for down bags; regular gentle detergent for synthetic. Tumble dry on low with 2–3 clean tennis balls to break up down clumps. May take 2–3 cycles to fully dry. Store uncompressed in a large cotton storage sack (not in the stuff sack) to preserve loft.
Yes — a sleeping bag liner (silk, cotton or fleece) adds 3–15°C of warmth depending on material, turning a 3-season bag into a 4-season bag at a fraction of the cost of a new bag. Liners also keep the bag cleaner and extend the time between washes. A fleece liner adds the most warmth; silk adds the least but is the most packable and luxurious.