Your Sleeping Bag Rating Is Lying — Check the Pad Instead

Two Numbers That Contradict Each Other

Across our catalogue, the sleeping bags go down to -6°C. The pads top out at R-1.6.

Those two figures describe the same night, and they do not agree. A bag rated to -6°C assumes a pad that can keep the ground from taking your heat, and R-1.6 is not that pad. Anyone pairing the two is going to be cold, and is going to blame the bag.

Pad	R-value	Thickness	Weight	Price
Trekology UL80	1.6	10cm	560g	$45.99
Decathlon Forclaz MT500 Air	1.5 (ASTM)	5cm	510g	$49.00
Klymit Static V2	1.3	6.3cm	460g	$74.99

Every one of those is a summer number.

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Why the Pad Wins the Argument

A sleeping bag works by trapping air in loft. Lie on it and the loft underneath you compresses to nothing — the down or synthetic fill between your back and the ground is doing no insulating at all.

So the bag's rating describes the half of you facing upward. The half facing the ground is entirely the pad's problem, and the ground is a far better heat sink than the air is. On a cold night you lose more heat downward by conduction than upward by convection, which is why the pad, not the bag, is what decides whether you sleep.

This is also why the fix for a cold night is so often counter-intuitive: putting on more clothes helps less than putting something under you.

What the Numbers Should Be

Rough working figures:

• R-1 to R-2 — summer only. Ground above about 10°C.
• R-2.5 — the usual three-season threshold. Ground down to freezing.
• R-4 and up — expect frost, or you sleep cold.

R-values are additive, which is the useful property: an R-1.6 inflatable on top of an R-2 foam mat gives you R-3.6, comfortably three-season, for about $25 and 300g more.

That stacking trick is the single best-value move in the entire sleep system, and it is almost never what people buy. The instinct is to upgrade the bag, which costs three times as much and fixes the half of the problem that was already working.

The Standard Most Numbers Don't Cite

R-values only compare if they were measured the same way. ASTM F3340 is the standard that made that possible — before it, every brand used its own method and the numbers were not interchangeable.

Of the pads we list, exactly one states the standard: the Decathlon at R-1.5 (ASTM). The others give a number and leave the method unstated.

That does not mean the others are wrong. It means R-1.6 unqualified and R-1.5 ASTM are not the same claim, and if you are choosing between two pads a few tenths apart, the one citing the standard is the one you can actually rely on.

Reading a Cold Night Backwards

You were cold. Work out which layer failed:

1. Cold underneath, warm on top → the pad. Almost always the answer.
2. Cold all over, from the start → you went to bed cold. Eat something and do star jumps; a bag is not a heater, it slows the rate you lose what you already have.
3. Warm at midnight, cold at 4am → normal. Body temperature bottoms out in the early hours, and your kit is being asked for its maximum exactly when you have least to give it. Budget one rating step colder than the forecast for this alone.
4. Cold at the shoulders and feet only → the bag's cut or a missing draft collar, not its rating.

What to Buy, in Order

1. Closed-cell foam mat, ~$25. Adds roughly R-2. Cannot puncture. Doubles as a sit mat and a windscreen for the stove.
2. A pad with a stated ASTM R-value, if you are replacing rather than supplementing.
3. The bag, last. It is the most expensive item and the least likely cause.

The corollary for anyone shopping our sleep system round-up: a $325 quilt on an R-1.3 pad will sleep colder than a $100 bag on an R-3.6 stack. The pad is not the accessory.