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 to boot.
A mummy bag also has a snug hood you can pull around your head for extra heat retention.
Semi-rectangular sleeping bags
Core feature: more legroom + usable as a blanket
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.
Core feature: better in warmer climates + the most space
Rectangle shapes are as wide at the foot as they are at the shoulders. They give you the most amount of room and are a good choice for warmer climates, camping beds, car camping, or for when you want to share your sleeping bag with someone else.
Note: Make sure you pay attention to the max sleeper height of your sleeping bag as well. As a general rule of thumb, you should add 25–30cm on top of your height for maximum comfort.