Hoss resting in the sun.
According to Penn State University, "Many may ask why the horse’s coat covering is called hair and not fur. Animals with a coat covering that is denser were utilized in garments, hence those coat covering were called fur. The horse’s coat covering is not used in wearing apparel and therefore it is called hair."
PSU continued, "In normal conditions a horse’s hair coat protects them against the cold temperatures in winter and is replaced in spring with a lighter coat that is more easily adapt at drying out if the horse becomes over heated and sweaty.
"The horse actually has three different hair coats. A summer hair coat and two winter coat growths. In the fall the summer coat sheds out and as the horse’s body prepares for winter it produces the two different winter hairs. One is a short, thick layer, while the other is long hairs that will stick up and provide air spaces that serve as an insulating layer against cold winter temperatures."