What Do Sleeping Bag Season and Temperature Ratings Mean?

Originally published 2012

A sleeping bag could be one of your most important camping purchases — it has a major part to play in how much of a restful night you get and your energy for the next day. We're here to help you understand what the gobbledegook means and how to pick the right sleeping bag for you. It's worth pointing out that everyone sleeps differently — some are warm sleepers, some sleep a bit cooler — and your tent, sleeping mat, even metabolism and calorie intake will all be factors that affect your body heat.

There are lots of things to consider when buying a sleeping bag — synthetic vs down, shape, weight — but perhaps the most important consideration is the temperature rating. How warm will you actually be?

Temperature rating

There is a European Standard for sleeping bag temperature ratings, EN13537. Key to this rating is that it is legal (in the EU) for sleeping bags to be labelled in a specific way. The standard requires manufacturers to run a thermal manikin test on their sleeping bags to measure four temperature ratings, in degrees Celsius:

• Upper Limit — the temperature at which a standard man can sleep without excessive perspiration. Established with the hood and zippers open and the arms outside the bag.
• Comfort — the temperature at which a standard woman can expect to sleep comfortably in a relaxed position.
• Lower Limit — the temperature at which a standard man can sleep for eight hours in a curled position without waking.
• Extreme — the minimum temperature at which a standard woman can remain for six hours without risk of death from hypothermia (though frostbite is still possible).

For the purposes of the manikin test, a standard man is 25 years old, 1.73m tall and 73kg; a standard woman is 25 years old, 1.60m tall and 60kg.

So with these temperatures you can pick the right bag for your expedition. However, for the more casual camper you may want a less technical guide to find something that's a good all-rounder — that's where seasons come in.

Seasons

Seasons are a less technical rating system for bags. All sleeping bags must carry the above temperature ratings by law (in the EU), but for marketing or guidance the retailer may also use a season rating. As this isn't regulated, there may be different interpretations of seasons. The below is a generally accepted guide:

• 1 Season (+5°C) — good for summer use only, comfortable above +5°C.
• 2 Season (0°C) — for spring/summer use, comfortable right down to 0°C.
• 3 Season (-5°C) — perhaps the most popular, a good all-round choice for most campers, comfortable to -5°C.
• 4 Season / Winter (-10°C) — comfortable as low as -10°C.
• 5 Season / Expedition (-15°C) — used in extreme conditions, comfortable as low as -15°C.

Our advice? Use both these sets of information together. First think about when and where you are likely to camp and use your sleeping bag — this gives you a season guide. Then identify the temperature specifications you need from that. Just remember, if you go for a winter bag or one with a low limit, check the comfort limit too — if it's too low you may get very hot if you also do a lot of summer camping. If that's the case, consider a lighter sleeping bag and a fleece liner for the colder months.