The Kuhl Men's Spyfire Down Vest uses a high 24 filament 20 denier ultra-fine nylon yarn (for a softer hand feel and higher tear strength). The yarn is then woven into an extremely dense weave that provides both excellent down-proof-ness and increases the already higher tear-strength. The 800 fill (certified non force fed / not live plucked) goose down is also body mapped: Different size baffles create superior warmth where you need it, while the smaller baffles reduce bulk for layering under a shell. The precision 3-D fit naturally follows the body and the intricate patterning and construction eliminate the binding which is typically found on the inside side seams of ordinary down sweaters. Four unique fabrics differentiate the KÜHL Spyfire from all others. Each fabric is engineered for a specific purpose. The soft shell reinforced fabric on the shoulders allows you to shoulder skis with sharp edges that would shred any ordinary down sweater. Light weight underarm knit fabric panels provide greater comfort in a wide variety of temperature by allowing heat to escape when you are more active.