A cold night is rarely about the sleeping bag alone. Warmth comes from three things working together: the mat under you, the bag around you and what you're wearing. Get the mat wrong and the best bag in the world won't save you.
Why the mat matters most
You crush the insulation underneath you when you lie on a sleeping bag, so it does very little there. The mat does that job. Cold ground pulls heat out of you all night, and a thin or uninsulated mat lets it.
What R-value means
R-value measures how well a mat resists heat escaping into the ground. Higher is warmer. Most brands now test to the same standard, so you can compare mats directly.
- Around R2 to R3: summer camping in mild weather.
- R4 and above: spring, autumn and colder nights. Our usual recommendation for the UK.
- R5 and above: winter and frozen ground.
Every mat we hire is insulated: the Big Agnes Divide Insulated is R4 and the Rapide SL Insulated is R4.8. See our sleeping mats.
How sleeping bag ratings work
Most bags are tested to a European standard that gives up to three temperatures:
- Comfort: the temperature at which a cold sleeper should sleep comfortably. This is the one to choose by.
- Limit: the temperature at which a warm sleeper can sleep curled up without waking cold.
- Extreme: a survival rating. Never plan to sleep at it.
Pick a bag whose comfort rating is at or below the lowest temperature you expect overnight. If you tend to feel the cold, go a few degrees lower again.
Seven ways to sleep warmer
- Eat something before bed. Your body needs fuel to make heat.
- Go to bed warm. A short walk beats climbing into your bag shivering.
- Wear a dry base layer, a hat and dry socks. Never sleep in damp clothes.
- Fill a bottle with hot water and put it in your bag.
- Pitch out of the wind, and avoid hollows where cold air collects.
- Shake your bag before you get in so the fill lofts up.
- Have a wee before bed. Your body wastes heat keeping it warm.
For cold trips, our Mammut Ajungilak Kompact is winter-rated, with synthetic fill that keeps working when damp.
