The Spire -4 Sleeping Bag is designed for cold-weather conditions, offering superior warmth with its body contour profile and OneThermo insulation. A 3D hood and redefined neck baffle help prevent drafts and heat loss. The shark fin foot box and full-length insulated zip baffle enhance insulation, while the brushed polyester lining ensures moisture control. Key features include an anti-snag YKK zipper, differentiated hood drawcords, inner pocket, compression stuff sack, and hanger loops.