A sleeping bag is a technical bit of gear. Depending on your activity, there’s a lot to consider. What should it be made of? Which is the best shape? And why are temperature ratings written in hieroglyphics?
If you’re new to sleeping bags, this guide will help you make the right decision when choosing the perfect fit.
Why you need to get it right when choosing a sleeping bag
Your sleeping bag plays an important role. In serious cases, choosing the right sleeping bag will protect you in very cold conditions and help protect you from cold-weather injuries. Beyond this, having the right sleep system when hiking or camping will have a range of effects:
Better sleep will improve your physical recovery each day and aid your post-hike recovery. Having a poor night's sleep reduces your body's production of cytokines, a protein that targets infection and inflammation.
The right sleeping bag, mat, and accessories will help prevent injuries the next day. Sleep plays a vital role in temperature regulation, fostering a strong immune system, steady hormone levels, and a good appetite. These attributes all form part of your energy and how you take on a hike each day.
Having a good night's sleep will simply put you in the right mental space for the next day.
How do you sleep?
How you experience the temperature is very personal. Some people just naturally run a little warmer or colder. Your sex can also make a difference. In general, women's internal clock can be slightly shorter than a full 24-hour cycle sleep that men experience, which means they can tend to wake up earlier and can also sleep at a temperature that is a few degrees colder than men.
You might also feel warmer or colder depending on a number of variables:
Weather conditions: High humidity, rain and snowfall will all affect how you experience the temperature while you’re in your sleeping bag. Factor in any variable weather conditions you may experience on your trip.
General sleeping conditions: Are you sleeping on a sleeping mat? You should be! Laying directly on the floor of a tent will be uncomfortable and cool you down as you lose heat through the ground. Similarly, how you experience temperature will differ between a hut and a tent.
The layers you wear to bed: Typically you shouldn’t wear too much to bed. If it’s cold, a thin base layer with some good socks and a beanie is usually enough. A sleeping bag liner can add another layer of insulation if you need it and keep your sleeping bag clean.
Fuel: If you go to bed on an empty stomach, you’re more likely to feel the cold. Make sure you fuel your body properly so you can generate enough heat – eat well and stay hydrated.
Choosing your sleeping bag's temperature rating
Most technical sleeping bags follow the European Standard EN13537 to communicate their temperature ratings. This includes three unique temperature categories: T Comfort, T Limit and T Extreme. When assessing a sleeping bag, look at what temperatures the sleeping bag suits based on the following:
T Comfort: Comfort is based on a ‘standard’ adult woman having a comfortable night’s sleep. She’s wearing one base layer in a relaxed position and, you guessed it, she’s comfortable.
T Limit (AKA the lower limit of the Transition range): is based on the lowest temperature at which a ‘standard’ adult male is deemed to be able to have a comfortable night’s sleep. He's also wearing one base layer but sleeps in a curled position to keep warm.
T Extreme (AKA the lower limit of the Risk range): is a survival-only rating for a ‘standard’ adult woman. This is an extreme survival rating only and it is not advisable for anyone to rely on this rating for general use. There will be a strong sensation of cold which can only be endured for a limited time.
In other words, you will choose a sleeping bag based on what temperatures you are likely to experience, and look at ensuring that you will sit within that 'T Comfort' stage.
These temperature ratings are represented on the example below:
To choose the right temperature, always base your purchase on the coldest temperature to expect during your trip.
If you’re um-ing and ah-ing over what the weather may or may not do, err on the safe side. Temperature expected to be 5 degrees? Go for 0.
It’s a lot harder to increase your warmth than it is to cool down. In short, you should always aim to choose a sleeping bag in the Comfort or Transition ranges depending on your individual needs.
How to choose a sleeping bag shape
Sleeping bags come in mummy, semi-rectangular or rectangular shapes. All come with distinct benefits.
Mummy sleeping bags
Core feature: maximum insulation + minimum volume and weight.
The mummy shape is narrow at the feet and tighter around your body so there’s less space around you. This is a deliberate design decision — with less empty space to heat up, your body won’t have to work as hard to stay warm. You’ll stay warmer for longer and use up less energy.
A mummy bag also has a snug hood you can pull around your head for extra heat retention.
These bags suit a variety of uses and temperatures and have a tapered cut that still provides efficient heat retention. There’s more space for your legs for those who like to sleep on their side or who move around more in their sleep. Unlike the mummy, you can open it up and use it as a blanket which can be beneficial in warmer climates.