The Fernos Insulated Jacket is a synthetic midlayer built to regulate warmth as effort changes. Its PeakFill(R) Active insulation uses a spiral filament structure that recovers loft faster and dries quicker than traditional insulation, so the jacket adjusts to activity instead of overheating once the pace picks up. The Relance(TM) Primeflex shell adds mechanical stretch through the shoulders and arms, and a Regular Fit keeps the cut easy to layer under a shell or wear on its own. What Our Gearhead(R) Experts Are Saying:"I split wood in this on a fifteen-degree morning and never had to shed it, even once I was moving fast enough to work up a sweat. It just seems to let the heat out as I need it to."