Ridgeline sleeping bags are designed for users whose utmost concern is performance. Each bag has a slim silhouette which provides the best thermal efficiency. The improved design includes a performance-style fully sculpted hood unique triangular draft tube and an angled trapezoidal foot section. The bags are constructed with an "uphill" shingle method which naturally increases loft as the bag is pulled over the shoulder and more loft means greater warmth. Overall this series provides the most thermal efficient design.