Brushed Inner Lining
The bag’s lining is brushed for extra softness, like a flannel sheet. Some folks like the extra coziness and wicking properties, while others complain that brushed linings are oppressive in hot weather and snag on dry skin and ragged toenails.
The outer shell is bigger than inner lining and allows insulation to loft as much as possible.
The fuzzy plumules found under a goose’s outer feathers and inside many sleeping bags. Down offers unbeatable loft, warmth, and compactibility, but it does not insulate when wet.
This water-resistant/breathable shell fabric will help your bag shed wind, condensation, light rain, and spilled soup, but doesn’t breathe as well as most taffeta or microfiber shells. It’s ideal for those who frequently sleep under tarps, in snow caves, or in generally wet conditions.
These synthetic insulations will perform similarly to others, but are heavier and bulkier than newer versions, which is why they typically are found in less expensive bags.
An insulated hood that can be cinched down around your head and face is an essential feature for reducing heat loss in all but the most temperate weather.
A piece of material with velcro that secures the zipper and prevents unplanned midnight unzippings.
Lite Loft, MicroLoft, Primaloft, Primaloft 2, Thermolite Extreme
These synthetic insulations come closest to the softness and warmth of down per pound, but they lack the durability. Known as "short-staple" fibers, they are lighter and compress better for packing than Hollofil, Quallofil, and Polarguard.
Lighter, more supple, but less water resistant than DryLoft (and also less expensive), microfibers are tightly woven nylon or polyester fabrics that breathe well, yet still turn back wind and resist light moisture.
The most popular sleeping bag design for backpackers, a mummy bag has a close-fitting hood and a tapered cut from shoulder to toe. The taper reduces dead air space for maximum thermal efficiency–your body has less volume to heat–and eliminates needless extra ounces.