How to choose a sleeping bag – the short answer
Choose a sleeping bag for the lowest night-time temperature you will actually sleep in, and look at the comfort rating, not the biggest number on the label. Second – and just as important – is the mat: without one, even a warm bag loses its heat to the ground overnight. Third come weight and packed size, because the bag has to fit in your backpack.
Where to start
Answer two questions: what time of year you will be sleeping outdoors, and whether you will carry the bag yourself or it will travel by car. The first answer decides the warmth; the second decides how much weight and bulk you can afford.
What the temperatures on a sleeping bag mean
The more serious manufacturers rate their bags to the ISO 23537 standard (formerly EN 13537). It gives three numbers, and each one means something different:
- Comfort – the temperature at which a standard adult woman sleeps comfortably in a relaxed position. This is the number to go by if you feel the cold easily.
- Limit – the lowest temperature at which a standard man, curled up, can sleep for eight hours. If you sleep warm, you can go by this one.
- Extreme – the survival limit. At this temperature you don't sleep; you wait for morning at risk of hypothermia. Never plan around it.
An example from the catalogue: the Tac Maven Winter Sleeping Bag 360 g/m² says to −18 °C in its name, but that is the extreme rating. Its comfort rating is −3 °C. The gap between those two numbers is the gap between a good night's sleep and a very long night.
One more nuance: not every manufacturer measures the same way. M-Tac gives its sleeping bags a temperature range (e.g. −5 to +5 °C) rather than the three standard numbers. You can't compare that kind of range directly with an ISO comfort rating – treat it as a rough guide.
By season: what to choose
Summer and warm nights
Tac Maven Cocoon Summer 80 g/m² – comfort +20 °C, limit +15 °C, weight 750 g. It's the lightest bag in the catalogue, mummy-shaped, with a compression bag. On a cool August night it will no longer be enough.
M-Tac Summer gives a range of 0 to +15 °C, weighs 1.2 kg and is 235 cm long. A side zip with two sliders lets you open it up when it's warm.
Spring and autumn
Tac Maven Major 370 g/m² – comfort +10 °C, limit +5 °C, extreme 0 °C, around 1500 g. Rectangular, with a two-way zip: room for your feet, and you can unzip it fully and use it as a blanket.
The M-Tac sleeping bag with compression sack gives a range of −5 to +5 °C. The fill is double-layer holofiber, 150 g/m², the shell is ripstop nylon, it weighs 1800 g and the zip has a wind flap.
The Mil-Tec Pilot stands out in a different way: it has a cotton lining, and its zip lets you join two bags into one. It weighs 1700 g and is 185 cm long – a taller person may find it too short.
Cold and winter
Tac Maven Winter Sleeping Bag 360 g/m² – comfort −3 °C, 1850 g, double-layer microfibre fill, YKK zip, compression bag. Mil-Tec SB2 two-layer mummy – comfort −5 °C, extreme −10 °C, 2000 g. The same model is also available in a woodland pattern.
To be straight with you: there is no sleeping bag in the catalogue with a comfort rating below −5 °C. For a colder night, build your warmth from several parts – the bag, a warm mat underneath it and dry clothes. It's the same logic as dressing in layers, which we explain in the guide on how to layer clothing for cold.
Shape: mummy or rectangular
A mummy bag tapers towards the feet and has a hood. Less air inside means less to heat, so the same insulation keeps you warmer in a mummy. The price is a tight fit: you can only turn over together with the bag.
A rectangular bag is roomier and more comfortable if you sleep on your side or with your knees drawn up. You can unzip it and use it as a blanket. In the cold it is less efficient: you have to heat the empty space around your feet with your own body.
Fill, and what g/m² means
Every sleeping bag in the catalogue has synthetic fill – hollow fibre, holofiber or microfibre. When it gets damp, synthetic fill holds its warmth better than down and dries faster, which makes it a good match for a Baltic autumn. The drawback is more weight and bulk for the same warmth.
The g/m² figure tells you how much fill there is per square metre. Between models from the same manufacturer it helps you compare warmth, but between different manufacturers the temperature rating is more reliable.
The mat: half your warmth comes from below
The fill underneath you gets squashed and barely insulates at all. What keeps your heat from draining into the ground is the mat. That's why, on a cold night, people often get cold not because the bag is too thin, but because there is nothing under it.
- Fox Outdoor Thermal Pad – a folding EVA foam mat, ~400 g. There is nothing to puncture, and it works in any conditions.
- M-Tac 15 mm – a 180 × 60 cm foam mat.
- Mil-Tec self-inflating mat – 186 × 53 × 2.5 cm, 876 g. Softer, but vulnerable to punctures.
- M-Tac inflatable pad 195 × 120 cm – 120 cm wide, 1000 g.
A mat's warmth is measured by its R-value: the higher it is, the better the insulation. None of these mats has an R-value listed in our catalogue, so for winter the most reliable approach is two mats, one on top of the other: foam at the bottom, inflatable or self-inflating on top. You'll find them all in the sleeping mats section.
Weight and packed size
The sleeping bags in the catalogue weigh from 750 g to 2 kg. Carried all day, a kilogram's difference is felt more than it seems in the shop. Packed size matters even more: the Mil-Tec two-layer bag packs to 45 × 45 × 68 cm – a bag that size goes in the car or gets strapped to the outside of a large backpack.
A compression sack, such as the M-Tac Compression Sack Large, reduces the volume but not the weight. How to pack heavy and bulky items in a backpack is covered in the guide on how to choose a tactical backpack.
Frequently asked questions
Is a sleeping bag rated "to −18 °C" good for winter?
Check which number that is. If it's the extreme rating, you'll only sleep comfortably at the comfort temperature – for the Tac Maven winter bag, −3 °C. Below that you need extra warmth: a better mat, warm clothes or a second sleeping bag.
Can one sleeping bag work for every season?
Only with a compromise. A warm bag is too hot in summer, although a zip you can open up partly solves that. People who sleep outdoors often usually have two: a light one for warm weather and a warm one for the cold.
Should you sleep in your clothes?
In dry, thin clothes – yes. In the ones you've been sweating in all day – no: the moisture chills you at night and dampens the fill. Change into dry clothes before you go to sleep.
How should I store a sleeping bag between trips?
Not in a compression sack. Fill that stays compressed for a long time loses some of its loft, and some of its warmth with it. Keep the bag unrolled or in a loose sack, somewhere dry.
A quick way to choose
- Work out the lowest night-time temperature you'll be sleeping in.
- Choose a bag whose comfort rating (if you feel the cold) or limit rating (if you sleep warm) is no higher than that.
- Add a mat – two in the cold.
- Check the weight and packed size against how you'll carry it.
You'll find every model in the sleeping bags category. If you're not sure which one suits your trip, write to us – we'll give you a specific answer.