Sleep System Picker
Bag rating and pad R-value for the forecast low — with an honest check on whether the gear you own is actually rated for the night you have planned.
What you need
Check the gear you already own
The rating on the label is probably not the one you want
Standardised bag testing produces several numbers. Comfort is the temperature at which a cold sleeper is genuinely comfortable. Limit is where a warm sleeper is curled up but not shivering. Extreme is a survival figure and has no place in trip planning at all.
Bags are usually marketed on the limit rating because it is the colder, more impressive number — and it sits roughly 12°F below comfort. So a bag sold as a "20 degree bag" is realistically comfortable to about 32. This single gap accounts for an enormous share of cold nights, and for the widespread belief that one's bag "doesn't live up to its rating".
A caveat worth stating: nobody's comfort is exactly average. Metabolism, hydration, whether you ate before bed, how damp your clothes are and how long you sat still in camp all move the real figure. Treat the numbers as a starting point and adjust from your own experience of past nights.
The pad matters more than people expect
Insulation compressed underneath you does almost nothing — the down or synthetic fill on the bottom of your bag is flattened to nothing by your own weight. Practically all your insulation from the ground is the pad, which is why people who are cold at night so often buy a warmer bag when the pad was the problem.
R-values add, and this is the most useful thing to know about them: a foam pad at R 2 under an inflatable at R 4 gives you R 6. Winter campers stack pads for exactly this reason, and also because if an inflatable punctures at −20°F, the foam pad underneath is what gets you through the night.
R-value by overnight low
| Overnight low | R-value | Notes |
|---|---|---|
| Summer 50°F and up | R 2 | Warm ground barely takes heat from you. Almost any pad will do; a foam pad at R 2 is plenty and cannot puncture. |
| Mild three-season 32°F to 50°F | R 3 | Below about 50°F the ground starts pulling real heat. R 3 is the point where most people stop waking up cold from underneath. |
| Cold three-season 20°F to 32°F | R 4.5 | Near and below freezing, insulation underneath matters more than the bag. R 4 to 5 is the standard shoulder-season answer. |
| Winter 0°F to 20°F | R 5.5 | Frozen ground is a heat sink. R 5.5 or more, and many winter campers stack a foam pad under an inflatable for redundancy as much as warmth. |
| Deep winter and snow -40°F to 0°F | R 7 | On snow, R 7 and up, almost always as two pads. If an inflatable fails at −20°F, the foam pad underneath is what gets you through the night. |
Down or synthetic
Down: Lighter and far more compressible for the same warmth, and it lasts decades if looked after. It also loses most of its loft when wet, which is the entire argument against it.
Synthetic: Heavier and bulkier, but it keeps a usable amount of warmth when damp and costs less. The right choice for persistently wet climates and for anyone hard on their gear.
How to use
- Find the forecast overnight low, not the daytime temperature.
- Read the suggested bag rating and pad R-value.
- Check your own gear against both.
- Remember the pad matters as much as the bag.
Frequently asked questions
Does a bag's rating mean I will be comfortable at that temperature?
Often not, and this misleads a great many people. Under the EN and ISO standards a bag carries both a comfort rating and a lower limit, and the number on the label is frequently the limit — the temperature at which a sleeper is expected to survive curled up, not sleep well. Buy on the comfort figure.
Why does the sleeping pad matter so much?
Because the insulation underneath you is compressed to nothing by your own weight, so the bag does almost nothing there. Conduction into cold ground is a major route of heat loss, and an excellent bag on a summer pad is a cold night. R-value is the number that matters, and it is additive if you stack pads.
What R-value do I need?
Roughly, 2 or below suits warm nights, around 3 to 4 covers three-season use, and 5 or above is for genuinely cold and winter conditions. R-values became comparable between brands only after a standardised test was adopted, so older published figures are not reliably comparable.
Do men and women need different ratings?
The standards produce separate figures because the average tested sleeper differs, and many people sleep colder or warmer than any average. The practical approach is to know your own tendency and adjust — someone who sleeps cold should treat a comfort rating as optimistic.
Down or synthetic?
Down is lighter and packs smaller for the same warmth and lasts longer if cared for. Synthetic keeps insulating when wet and costs less. In persistently damp conditions, or where drying out is impossible, synthetic's failure mode is far kinder — a soaked down bag is very close to no bag at all.
What else changes how warm I sleep?
Eating before bed, wearing dry clothes rather than the damp ones you hiked in, a hat, a hot drink, and not going to bed already cold. Ventilating the tent to reduce condensation matters too, since a damp bag insulates worse — the gear is only part of the answer.
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