Every few months a customer asks us why our flagship -10°C bag uses synthetic insulation instead of premium goose down. The honest answer is that we tried both, and the synthetic won — but only because we spent two years building a fill that doesn't behave like normal synthetic.
The down problem in India
Down is brilliant at trapping air with very little weight. 850-fill goose down is the gold standard — warmer per gram than anything else humans have figured out. But it has one catastrophic weakness: when down gets wet, the clusters collapse, and a wet down bag retains roughly 10% of its dry warmth.
In the Indian Himalaya this happens more than people admit. A wet tent floor, condensation dripping from the inside of a single-wall shelter, a monsoon-tail storm in September, sweat on a hard climb that soaks the bag from the inside — any one of these can ruin a down bag for the rest of a trip. Re-lofting takes hours of sun, and at altitude you rarely get hours of sun.
What Supra-Loft does differently
Supra-Loft is a continuous-filament siliconised polyester. The fibres are extruded as long strands rather than chopped staples, which means the loft doesn't migrate or clump after compression. Each fibre is hollow and siliconised, which traps air and shrugs off water — a soaked Supra-Loft bag retains around 85% of its dry warmth and dries in roughly 90 minutes hanging over a pack in the sun.
The trade-offs we accept
- Weight: our -10°C Supra-Loft bag weighs 1.45 kg vs roughly 1.0 kg for the equivalent 800-fill down bag
- Pack size: 30% larger compressed
- Longevity: Supra-Loft loses about 15% of its loft after five years of regular use; quality down keeps its loft almost indefinitely if you look after it
When we'd recommend down instead
If you trek primarily in dry, cold conditions (winter Spiti, Zanskar in February) and you obsess about pack weight, down still wins. We sell a down bag for exactly that customer. But for the 90% of people doing summer and shoulder-season trips in the Indian Himalaya, where moisture is the bigger enemy than weight, the extra 450 grams of synthetic is the cheapest insurance you'll ever buy.