Poncho liner

A poncho liner is a piece of field gear originating in the United States military intended to provide warmth in mild temperatures used as a field expedient sleeping bag when attached to the standard issue poncho by means of integral lengths of material which are looped through the poncho's eyelets.

Construction
The poncho liner consists of two layers of quilted nylon encasing a polyester loft filling. Most examples are a variation of olive drab on one side and camouflage on the other, either ERDL pattern in earlier examples or the later Woodland pattern, as well as the MARPAT and Universal Camouflage Pattern most recently. Commercial copies include features like thinsulate batting, a zippered edge and come in a greater range of colors

Opinions amongst the troops
Troops generally hold the poncho liner in high regard, as a very useful piece of equipment, light and packable yet reasonably warm. Some military personnel refer to the poncho liner as a "woobie" showing the same attachment an infant has for its blanket. Many servicemen and women go through great lengths to find ways to keep their poncho liners as long as possible, even after they have left the military. The poncho liner found wide acceptance amongst US troops in Vietnam, providing just enough warmth for cool tropical nights but light and small. It is especially popular today in the age of 100-pound rucks and bulky Modular Sleep Systems.