Silk sleeping bag liners are the nicesttheyre soft, compact, add a little warmth to a sleeping bag or bed, and can be used as a stand-alone sleep cover in very warm climates. A good example is the Cocoon Ripstop Silk Bag Liner/Travel Sheet, which sells for $65 (cocoon.at). Cocoon Ripstop Silk Bag Liner Cocoon Ripstop Silk Bag LinerCotton liners work pretty well for everyday use. Cocoons cotton version of its silk bag liner goes for $20. Wool is popping up everywhere, and you now can purchase a Merino wool bag liner from REI for $65 (rei.com).