ALPS Mountaineering Fleece Bag

You can add a touch of extra insulation to your sleeping bag with the soft Alps Mountaineering Fleece Bag. The rectangular shape fits inside mummy or rectangular bags, and the polyester fleece provides warmth without adding a ton of bulk to your backpack. You can even use it on its own if you're sleeping in warm spots, so you don't have to bring a big, heavy bag with you.