● Synthetic Thermawave polyester insulation is durable and highly compressible; synthetic polyester fill retains some insulating properties even when wet

● Shingle construction with overlapping layers distributes insulation evenly and keeps it from moving around so there are no cold spots

● Equally distributed insulation accommodates the multiposition sleeper; mummy shape is thermally efficient, yet roomy enough to ensure sleeping comfort

● REI Lumen +40°F sleeping bag has a relaxed fit through the shoulders and hips, giving you room to move for a better night's rest

● Ripstop nylon shell fabric has a nice hand feel, and is lightweight, durable, water- and abrasion resistant; nylon taffeta lining is soft and tear-resistant

● Shell fabric is treated with a Durable Water Repellent finish to repel moisture and stains

● Contoured hood, insulated full-face muffler and full-length zipper draft tube with ground-level seams work together to keep heat in and cold out

● REI Lumen +40°F has an external chest pocket to keep small essentials—headlamp, watch, glasses—right at hand and easy to find in the dark

● Special pocket in hood can be stuffed with clothing layers to make a pillow that stays in place; no need for a pillow to take up valuable space in your backpack

● Pad loops provide attachment points to keep your sleeping bag and pad together to avoid rolling off onto the cold ground (straps and sleeping pad sold separately)

● Full length zipper is backed by wide, antisnag binding tape

● Any REI backpacking bag can be zipped to any other REI backpacking bag because of the consistent 63 in., No. 5, YKK zipper; women's bags zip on the right, men's on the left

● Differentiated drawcords (1 round, 1 flat) allow quick identification, even in the dark, so neck and hood adjustments are a cinch

● Nylon stuff sack and cotton storage bag included

● Tested by an independent third-party lab using European Norm protocol, the EN temperature ratings allow direct comparisons across brands with other EN-rated bags