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 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).