Guide 3 min
Down or synthetic: how much weight at equal comfort?
At 0 °C comfort, a down sleeping bag weighs 930 g and its synthetic twin 1670 g: a 740 g gap. Real pairs from the catalogue, compared to the gram.
At equal comfort, down weighs less than synthetic: 180 g to 860 g less, depending on the bags you compare. At 0 °C comfort, the gap is 740 g between two bags from the same brand. You don't read it on the "down" or "synthetic" label: you read it on the scale, pair by pair.
We took the sleeping bags in the WildKit catalogue and sorted them by comfort temperature. Wherever a down bag and a synthetic bag share the same comfort rating, we weighed the gap. No "best bag", just grams.
How much less does down weigh than synthetic at equal comfort?
180 g to 860 g less, depending on the pair. The catalogue holds twenty sleeping bags, fourteen down and six synthetic. Three comfort temperatures bring both fills together: enough to compare at equal warmth.
| Comfort | Down | Synthetic | Gap |
|---|---|---|---|
| 0 °C | Forclaz MT900 down, 930 g | Forclaz MT500 synthetic, 1670 g | 740 g |
| 0 °C | Cumulus Panyam 450, 810 g | Forclaz MT500 synthetic, 1670 g | 860 g |
| -1 °C | Sea to Summit Ascent, 840 g | Nemo Forte 20, 1020 g | 180 g |
| -1 °C | Sea to Summit Trek TkII, 940 g | Rab Solar Eco 2, 1150 g | 210 g |
So the gap isn't a constant. It depends on the two bags you put side by side, not only on their fill.
At 0 °C, synthetic weighs 740 g more
This is the clearest pair: same brand, same comfort, two fills. The MT900 down weighs 930 g, the MT500 synthetic 1670 g. You carry 0.74 kg more to sleep at the same temperature.
Against the Cumulus Panyam 450, also down, the gap rises to 860 g: 810 g against 1670 g.
At -1 °C, the gap shrinks to 180 g
Among bags rated -1 °C comfort, synthetic gets much closer. The Nemo Forte 20 weighs 1020 g, the Sea to Summit Ascent in down 840 g: a 180 g gap. The Rab Solar Eco 2 weighs 1150 g, the Sea to Summit Trek TkII 940 g: a 210 g gap.
A well built synthetic bag can stay within 210 g of a down one. Don't choose on the fill alone: compare the real weights.
Can a down bag be both lighter and warmer than a synthetic one?
Yes: the Cumulus Lite Line 300 in down weighs 600 g for 4 °C comfort, the Forclaz MT500 synthetic 970 g for 10 °C. The down bag is 370 g lighter, that is 0.37 kg, and its comfort goes 6 °C lower.
| Bag | Fill | Comfort | Weight |
|---|---|---|---|
| Cumulus Lite Line 300 | down | 4 °C | 600 g |
| Forclaz MT500 | synthetic | 10 °C | 970 g |
Here, synthetic saves neither grams nor warmth. If it wins on anything, it isn't the scale.
And in your backpack?
A sleeping bag takes about 8 L/kg once packed: the 0.74 kg gap of the 0 °C pair means close to 5.9 L of extra space. The full calculation lives in what actually fills your wild camp bag.
What to remember
- At equal comfort, down weighs 180 g to 860 g less than synthetic in the catalogue.
- At 0 °C, two bags from the same brand: 930 g in down, 1670 g in synthetic, a 740 g gap.
- At -1 °C, the gap drops to 180 g or 210 g: compare real weights, not the label.
These grams count in the total you'll carry, next to the tent, the mat and the water (see how much your bag should weigh). Give your trip to the configurator: your sleeping bag shows up with its weight, already counted in your pack.
A guide WildKit keeps up to date. Published .