Guide 4 min
Cold at night wild camping? Match your bag and mat
Cold at night wild camping? The cold rises from the ground. Match bag and mat to the night: -9 °C means comfort under -9 °C and an R4 mat.
You're cold at night and you can't tell if it's the bag or the mat. Usually both, because cold reaches you by two routes. The air is the sleeping bag's job. The ground, which pulls your heat out all night, is the mat's job, and it's the one people forget most. So you don't pick one then the other at random: you match them together, from a single figure, the temperature of the night ahead of you.
Most pages cover the bag on one side, the mat on the other, and never start from a night figure. WildKit does the opposite: it works out the night first, then sets both items at once for that night.
Work out the night ahead first
A night is calculated, not guessed. Start from a seasonal temperature, then take off the cold you gain with altitude:
- spring: 0 °C
- summer: 10 °C
- autumn: 0 °C
- winter: -5 °C
Every 1000 m takes off 6 °C. The formula fits on one line: night = seasonal temperature minus 6 °C for every 1000 m of altitude.
One example we'll use for the whole guide: in spring, at 1500 m, the night comes to 0 - 6 x 1.5 = -9 °C. It's this figure, and this figure alone, that triggers the two choices below. No need for a big table: a good estimate of the night is enough.
The bag is chosen on its comfort temperature
A bag carries a comfort temperature: the one at which an average sleeper gets through the night without shivering. The rule is simple: aim for a comfort at or below the night you worked out. For our -9 °C, you need a bag that's comfortable below -9 °C.
But don't grab the warmest one on the shelf either. A bag oversized by more than 8 °C below the expected night is ruled out: too warm (you sweat, then you're cold), and above all too heavy and too bulky for nothing. Below -9 °C, you stay above -17 °C or so. The right window is narrow, and that's on purpose.
The mat is chosen on its R-value
The same night, this time read as insulation from the ground. The R-value says how much the mat cuts you off from the cold rising out of the earth. The lower the night goes, the higher the R has to climb:
| Night worked out | R-value to aim for |
|---|---|
| Below -10 °C | R ≥ 5 |
| Below 0 °C | R ≥ 4 |
| Up to 10 °C | R ≥ 2 |
| Above 10 °C | R ≥ 1 |
These are thresholds, not a conversion: an R-value doesn't translate into exact degrees. For our -9 °C, we're below 0 °C but above -10, so R4. An R2 would do you for a summer night at 10 °C, never for this one.
How do you match a sleeping bag and a mat?
Choose both from the same night figure, in a single move. Here's the heart of it. On -9 °C, your setup isn't "a good bag" or "a good mat": it's the pair comfort below -9 °C AND an R4 mat, chosen in a single move. A perfect bag laid on an R1, and the ground wakes you in the middle of the night. An R4 under a summer duvet, and it's the air that wakes you. The two hold together, or they don't.
The match also plays out in volume and weight. Sleeping gear is the bulkiest part of the bag: reckon on around 8 L per kilo for the sleeping bag, 6 L per kilo for the mat. Going up in warmth and R means going up in litres and grams, and the target for a wild camp stays 8 kg base weight. Choosing the two together is also how you hold that space and that weight (see What backpack volume, How much your bag should weigh and Is a 40 L bag enough for a wild camp).
Related guides
- What backpack volume for a day hike, a wild camp, a trek?
- Is a 40-litre backpack enough for a wild camp?
- What budget for a day hike, a wild camp, a trek?
What to remember
- Work out the night first: seasonal temperature minus 6 °C for every 1000 m. Everything starts from this figure.
- Match the two: a comfort ≤ the night, and an R-value drawn from the same threshold (R4 below 0 °C, R5 below -10 °C, R2 up to 10 °C).
- Sleeping gear is heavy and bulky (8 L/kg the bag, 6 L/kg the mat): keep the pair inside the 8 kg base weight.
A perfect bag on a mat that's too thin, and you shiver all the same, fancy label or not. It's also the most expensive part of a wild camp (see The cost of hiking gear), so best not to get it half wrong. Tell the configurator your season and your altitude: it works out your night and matches the bag and the mat to it, not to an average night. And if it's your first time out, keep the first-night wild camp checklist to hand.
Written by Thanaël Fontaine. Published .