Sleeping bags are one of the only products on the market that have a temperature rating. Think about it, you don’t buy a jacket with a temperature rating, or even a quilt for your bed at home.
If you’re feeling cold you put on an extra jumper or extra blanket on the bed. Despite this, we expect that a sleeping bag with a ‘temperature rating’ of 0 degrees will keep us toasty warm in the snow no matter what type of person we are.
The reality is that this temperature rating really is just a guide. We all feel the cold differently so we simply cannot expect a sleeping bag to be such an exact science, or that one temperature rating fits all. So, what does temperature rating mean? And, how can we use this roughly equated number to help us choose an appropriate bag for the job?
Think about the conditions where you’re planning on using your bag and if you’re generally a cold sleeper before you make your decision. Image: Sea to Summit
What temperature sleeping bag do I need?
Firstly, before delving in – you should ask yourself:
- Do you mainly go away when it’s cold? When it’s hot? Or both?
- If it’s going to be cold, how cold will it be? Is there a chance of frost or snow?
- Are you sleeping outside? In a tent? How big is the tent? Or maybe it’s just for sleepovers?
With those considerations in mind, let’s talk sleeping bag ratings.
+5 to +10 degree sleeping bag
A +5 to +10 is considered a summer bag. It is roughly as warm as sleeping with a sheet or light blanket over you on your bed at home.
0-degree sleeping bag
A 0 degree bag is a great all-rounder but won’t keep you warm in the snow or frosty night – it’s about the same as having a regular doona on your bed at home.
-5 to -10 degree sleeping bag
A -5 to -10 degree bag is considered a winter bag for typical Australian climates – it should be similar to having flannelette sheets and an extra blanket or 2 on your bed at home.
Top tips to help you choose a sleeping bag to keep you warm:
- The temperature rating is the point at which you will likely wake you up! You will feel cooler as the external temperature approaches this rated temperature, so it’s important to give yourself a temperature buffer.
- As a starting point, work out the lowest temperature you will be using the sleeping bag most of the time.
- From here, we recommend adding a buffer to ensure you sleep warm… this is dependant on how you sleep:
- Warm sleepers – refer to the the EN/ISO tested ‘Comfort’ rating as a starting point and choose a bag with this rating at 5 degrees below the lowest temperatures you plan to use your sleeping bag in.
- Cold sleepers – refer to the EN/ISO tested ‘Lower Limit’ rating as a starting point and choose a bag with this rating at 5-10 degrees below the lowest temperatures you plan to use your sleeping bag in.
- Keep in mind that you can expand the comfort range of a sleeping bag by adding liners for extra warmth or use the sleeping bag unzipped as a doonah to cater for temperature extremes you may encounter on occasion.
- Finally… this is not an exact science, we are all different with varying metabolisms. You’ll need to use some of your own best judgement in your selection.
These are all factors worth considering to help you select the right bag. If you want to understand how temperature rating is tested and measured, then read on.
Look out for sleeping bags that are marked with EN13537 – as that indicates they’ve been tested to an EU standard. Image: Sea to Summit
What does the EN/ISO temperature rating mean?
Sleeping bags have to be independently tested by the manufacturer to obtain the rating. The rating is often based on an R-value which is a measurement of insulation – just like the insulation in the walls of your house.
Some manufacturers will do real world testing on one sample of their insulation, and apply a formula to the different sleeping bags, whereas sleeping bags tested to an EN (European) Standard, or since 2016 an ISO or international standard are the most accurately tested bags.
Keep in mind though, that this testing is done in a controlled and static environment where a dummy is placed inside the sleeping bag with temperature sensors. So unless you’re a motionless dummy sleeping in an environment void of variables, you’ll need to make some allowances for your own physiological makeup and the equipment you are using.
What is the EN or ISO Standard?
There are no testing guidelines here in Australia, so look out for bags that have been tested according to EN Standards. The EN Standard for sleeping bags is marked EN13537 which was superseded by the ISO 23537-1 international standard in 2016.
The standard measures 3 temperature ratings:
Comfort – the temperature at which a standard woman can expect to sleep comfortably, without feeling cold and in a relaxed position.
Lower Limit – the temperature at which a standard man inside the bag sleeping in a curled position is starting to feel cold but not shivering, this is the limit of performance for the sleeping bag.
Extreme – at this temperature anyone can expect to feel particularly cold and there is a risk of hypothermia. You should only use the sleeping bag in this range when it’s an emergency.
Note: Not all manufacturers will list all 3 ratings, make sure you’re considering the correct one.
For example, Sea to Summit sleeping bags are all tested to EN Standards. Image: Sea to Summit
At the end of the day, no amount of laboratory testing is going to be 100% accurate for you. Cheaper sleeping bags will advertise a more generous rating that may not be accurate. Bags that list the EN/ISO Standards will be more accurate and provides a good point for comparison between bags. But as that process is expensive, it will affect the price tag.
If you want some advice on how to make your sleeping bag warmer in the winter months, then check out our guide here.
The last tip I’ll leave you with for selecting a temperature rating is: you can always shed a layer or unzip your bag if you’re hot, but if you wake up freezing cold in the middle of the night there won’t be much you can do to get warm!
What bag do you have and what rating do you find to be most versatile?
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