This versatile cap is wool lined with a cotton shell and Velcro fastened neck closure. Technically, it is a Cap, Cold Weather, Insulating Helmet Liner. It is thin but warm. With the flaps down, soldiers wore this under their helmets and the chinstraps passed through 2 small slits on the sides. It can be worn in several ways and also makes a great Hard Hat winter liner, or a cold weather anything Cap for extreme activities, snowboarding or snow blowing your driveway.
The Cold War era OD green variation is getting hard to find these days.