It is hard to find a single sleeping bag that meets all your needs all year round.
I own three. One is perfect for spring, autumn and early winter, a second for warm summer nights, and the third is built for extreme winter conditions. That keeps me cool but comfortable in summer, and snug and warm when I am out in winter at temperatures below minus fifteen.
The temperature ratings
The label always carries three temperatures: comfort, limit and extreme. That is confusing at first. Why three?
Comfort
The comfort rating is the lowest temperature at which the bag keeps the average woman warm.
Limit
The limit rating is the lowest temperature at which the bag keeps the average man warm.
Extreme
The extreme rating describes the worst case. It is effectively a survival figure for the average adult woman. At that temperature you will not be comfortable, but you will stay alive.
Sleeping bags are classified on that basis:
- Summer: plus 10 degrees and above
- Three season: plus 10 to minus 5 degrees
- Winter: minus 5 to minus 15 degrees
Those figures do assume you are wearing a layer of long underwear and that there is a sleeping pad underneath the bag.
Why the difference between women and men? A woman loses more body heat during sleep on average than a man. Your typical temperature also depends on your own metabolism, which varies a lot from person to person. There are differences between brands too, because manufacturers use different testing procedures.
So treat those figures as a guide, not a guarantee. Ideally choose a bag rated slightly lower than the temperature you expect. And remember that nights can cool down sharply even in summer. If it does get too warm, unzip the bag partly for some airflow.
The shape of the bag
The less air and space between you and your bag, the faster you warm up and the longer you stay warm.
Rectangular
The classic camping bags are rectangular and give you more room to move. Some zip together, which is cosy for couples. They do warm up less efficiently than mummy bags. So for an adventure with us, they are not the right buy.
Mummy bag
Mummy bags fit snugly around your body, though that varies by brand and model. They have a hood you can cinch down, so you do not lose heat through your head and neck.
Here too you see a difference between women's and men's models. Women's mummy bags are shorter, with narrower shoulders and wider hips, plus extra insulation around the torso and feet.
Do try a few models in the shop to find one that fits you well.
Which insulation should you choose?
There are two kinds of insulation: down and synthetic.
Down
Down lasts longer and is slightly warmer than synthetic filling. It also carries a higher price tag. On top of that, down is useless the moment it gets wet, and it takes a long time to dry. Some brands offer water resistant down, which works very well but costs more again.
Look for brands that work with certified down. The production process is kinder to the birds and means safer working conditions and fair pay for the people involved.
Synthetic
Synthetic insulation is usually polyester. It has plenty of advantages: it dries fast, lasts well, is non allergenic and costs less than down.
It does not compress as small, and those bags generally weigh a little more than down models.
Features to look at
The outer shell
The outer shell of most bags is made from sturdy ripstop nylon or polyester. Some have a water repellent coating.
The lining is designed to move moisture away from your body. That coating is not used on the inside.
The hood
If you sleep out in the colder months, you need a mummy bag with a hood and drawcord. That hood stops your heat from escaping.
Some hoods have a small pillow pocket you can fill with an inflatable pillow or a piece of clothing.
Inner pockets
Not for your secret sweet stash, but to keep valuables such as a watch or phone close. It prevents theft and keeps your devices warm in winter, so the battery lasts longer.
In cold environments you can also slip a chemical heat pack in there, close to your torso.
Accessories
Compression sack
Many bags come with a compression sack, and you can buy one separately too.
Get a waterproof one. Heavy rain soaking your whole pack, or a bottle left open: I have seen it all. Ideally choose one with compression straps so you can pack the bag as small as possible.
Storage sack
This is not the same as the compression sack. More expensive bags come with a roomy storage sack. It is large and lets the fabric breathe while the bag is not in use. Keeping your bag compressed for long stretches between trips costs you insulation.
Sleeping bag liner
A liner has the shape of a sleeping bag but no filling. They are made of cotton, silk or fleece, keep your bag clean and add a little warmth in cold conditions.
In warm conditions you can even skip the bag and sleep in the liner alone. Handy when you come down from an adventure in the mountains into a warm valley.
Hopefully this guide helps you find the right sleeping bag. Do keep in mind that a true all rounder does not exist. To sleep well all year round, you will want both a winter and a summer model.