If you're the dude who cuts his toothbrush in half, shaves his legs, and pulls out all his teeth to save weight before going backpacking, odds are you'll fall in love with the Marmot Plasma 40 Degree Down Sleeping Bag. It's pretty much a one season bag mild spring and fall nights will be OK, too, but good gravy, is it light and packable does 1lb 2oz float your boat' The Plasma's able to be so minimal because it packs super high loft 875 fill down into a Pertex Quantum shell, which is extremely durable but still light as a feather, and uses Insotect Flow vertical baffles to direct heat to your extremities. In that way it keeps your feet warm without the need for more down, which would just take up space in your pack. If it's not enough that the Plasma would pack into your water bottle, its down is treated with Down Defender to improve its water resistance, and the bag's exterior has a DWR coating to shed water and keep the insulation functioning with optimum efficiency. It also has a litany of desirable features, like an insulated draft tube and collar, two way zippers with garages, and a soft face muff to seal out drafts around your mug. Hang it up using the loops, store it in a loose sack to keep the down lofted, and you'll have ultralight summer insulation for years.