Thank you for viewing. This is a size S compression sack. It is used to compress luggage by covering a stuff sack containing a sleeping bag (schlafsack) or clothing and tightening it, making packing for mountain climbing and camping more efficient. This product uses "Ultra-Sil" nylon, which is lightweight, durable, and water-repellent. Size: S ■ Compatible Montbell sleeping bags (reference) Down Hugger 800 series: #2, #3, #5, etc. Down Hugger 650 series: #1, #2, #3, etc. Barrow Bag (synthetic fiber) series: Thin to medium-thick models such as #3, #5, #7, etc. ※ Size L is also available.