Sleeping Bag Temperature Ratings Explained

A sleeping bag's comfort rating is a useful comparison point, not a guarantee that you will be warm. Choose for the overnight conditions at your campsite and consider the sleeping mat, shelter and dry clothing as one system. Never use the extreme rating as the target for a planned night's sleep.

Comfort, limit and extreme

Manufacturers may publish several temperatures for the same bag. Before comparing products, check whether the figures use the same test method and which figure appears in the product name.

Rating	How to use it
Comfort	A starting point for choosing a bag, especially if you sleep cold
Limit	A lower test threshold, not equivalent to comfortable sleep for everyone
Extreme	Emergency-only territory, not a normal operating temperature

Therm-a-Rest's EN/ISO explanation makes clear that the extreme range involves a risk of hypothermia. A bag labelled with a very low number is not necessarily a comfortable choice at that temperature.

Laboratory reference sleepers are not individual predictions. Your fit, clothing, fatigue and the environment affect the result. Ask the manufacturer which figure is being advertised when the label is unclear.

Choose for a place, not an island

There is no single sleeping-bag temperature that covers a New Zealand summer. NIWA's climate overview describes strong differences between coastal, inland and mountain climates. A regional average is not a campsite's overnight forecast.

Check the elevation and forecast for your actual stop. Allow a margin for colder conditions and for your own experience of sleeping outdoors. Someone who routinely sleeps cold should not choose the same minimum rating as someone who has comfortably used a comparable system before.

For a first trip, choose an accessible campsite where you can leave or change accommodation if the setup is unsuitable.

Include the mat

A warmer bag cannot be judged separately from what is beneath it. Compare the mat's insulation information and intended conditions as well as its thickness and comfort. An air mattress chosen for cushioning alone may not provide the insulation you need.

Test the combination before relying on it somewhere remote. Check for leaks, take an appropriate repair kit and make sure the mat fits inside the tent without compressing the sleeping bag against wet walls.

Fit, fill and keeping bedding dry

Try the bag with the clothing you expect to wear. You should be able to move without compressing its insulation or leaving large uncomfortable gaps around the shoulders. Length, hood adjustment and zip access matter as well as the temperature label.

Compare down and synthetic models using their tested warmth, packed size, weight, care requirements and cost. Do not treat either fill as permission to let the bag get wet. Pack bedding in waterproof storage and keep wet clothing separate.

Follow the manufacturer's washing, drying and storage instructions. Check the bag's condition before departure, especially if it has been stored compressed or damp.

Before you go

• Check the exact campsite forecast and choose a suitable comfort rating.
• Confirm the mat's insulation and check for leaks.
• Pack dry sleeping layers and protect bedding from rain.
• Plan an exit or alternative accommodation if conditions exceed your system.
• Use the camping checklist and packing tool to check the complete kit.