Every time someone buys a puffy at the store, we have this conversation. Down or synthetic?
Down's case
Warmer per ounce. Compresses smaller. Longer lasting. A good 800-fill down jacket lasts 15 years.
Fill power tells you how lofty the down is. 600-fill is budget. 800-fill is mid-range. 1000-fill is top tier and mostly diminishing returns.
Down's weakness
Wet. Down loses almost all its insulation value when saturated. Modern hydrophobic down (DWR-treated) helps, but only delays the problem. It still collapses wet.
Not great for wearing while active. Down traps sweat, which eventually dampens the insulation from the inside.
Synthetic's case
Keeps some insulation value when wet. Handles abuse better. Cheaper. Holds up in humid, saturated conditions where down would fail.
Primaloft Gold is the best synthetic I've worn. Patagonia Nano-Air is a close second, with better breathability during activity.
Synthetic's weakness
Heavier for the same warmth. Doesn't compress as small. Loses loft over time, unlike down which can be restored.
Where I use each
Down for Southern Appalachian weekends where I'm moving between dry cabins or tents and cold mornings. Down for winter day hikes.
Synthetic for anything where I might be active and warm (hiking in cold rain), for alpine climbing where I need to move in it, and for trips where I can't guarantee the jacket stays dry.
Hybrid options
Some jackets (Patagonia DAS Light) use synthetic in high-sweat zones (armpits, back) and down everywhere else. These are cleverly designed and usually worth the price bump if you can swing it.
What I actually own
One mid-weight down (Patagonia Down Sweater, 9 oz), one synthetic active piece (Nano-Air), one heavy static down (Mountain Hardwear Ghost Whisperer UL). That covers 95 percent of what I do.
