Heavy Insulation

Fill power measures how much space one ounce of down occupies. Higher numbers like 800 or 900 mean the down is loftier and traps more air for its weight, giving better warmth-to-weight performance. Lower fill power (like 600) can still be warm but may require more down and result in a bulkier jacket.

Down offers the best warmth-to-weight ratio and compressibility but loses performance when wet. Synthetic insulation, like PrimaLoft or Coreloft, stays warm even in damp conditions and dries faster. For cold, dry expeditions, go down. For mixed weather or humid conditions, synthetic is often the better call.

Expedition parkas are built for sub-zero temperatures and extended exposure, not casual use. If you’re climbing cold, high peaks or standing still for long periods, a heavy parka is essential. For most summer alpine climbs, a midweight down or synthetic jacket is plenty.