Standard horse blankets are commonly kept on a horse when it is loose in a stall or pasture as well as when traveling. Different weights are manufactured for different weather conditions, and some are water-resistant or even waterproof. Modern materials similar to those used in human outdoor wear are commonly used in blanket manufacture.
Blankets are sometimes used to keep the horse's hair short. If horses are blanketed at the beginning of the autumn, especially if kept in a lighted area for 16 hours a day, they will not grow a winter coat. Blankets also protect horses that are kept with a short, clipped hair coat for show purposes. When a horse is given a full body clip, or even a partial "trace clip," it needs to have a blanket kept on at all times if the weather is cool because the horse no longer has the natural insulation of a longer hair coat. If a blanket is put on a horse at the beginning of the winter in order to suppress the growth of a winter coat, or if the horse is kept clipped in cold weather, the blanket it cannot be taken off until warmer weather arrives in the spring. If a horse is subjected to cold weather without either a blanket or a natural hair coat to keep it warm, it may become ill, vulnerable to sicknesses such as influenza.
Another type of horse blanket, called a Cooler, is literally a square blanket with ties that is draped over a horse that is hot and sweaty from an intense workout, or one that has just been bathed and is wet all over. It is kept on while the horse is being walked to cool down and allows enough air circulation for the horse to dry, but prevents chills and drafts from causing problems for the horse. It is tied shut in front, often with a small browband that keeps it positioned well up on the neck, and has a loose cord behind to prevent the wind from blowing it off from the rear, but usually has no other straps or attachments. It is intended to only be used on a horse while the animal is being led by a person and cannot be left on an unattended horse. In very windy weather, a loose surcingle may be added to prevent the cooler from blowing completely off.
Although heavy blankets for warmth make up the bulk of the horse blanket market, lightweight blanket may be used in the summer to help the animal ward off flies and to prevent the hair coat from bleaching out. Such blankets are usually called a "sheet" or a "fly sheet." They are usually made of some type of nylon or strong synthetic fiber, but with the capacity to "breathe" so that the animal remains cool. Most have a smooth nylon lining in front to prevent hair from wearing off on the shoulders. They are becoming increasingly popular, particularly with the rise of insect borne diseases such as West Nile Virus.
Any blanket may be supplemented with a neck cover or a full hood. Neck covers are often attached directly to the blanket. Hoods are a separate piece of horse "clothing," which cover the neck and come down the head to just above the muzzle of the horse, with holes cut for the eyes and ears. Summer weight hoods and neck covers help keep away insects and are also frequently used to keep a horse clean prior to a horse show. Winter weight hoods are used for warmth.
A blanket or pad used under a saddle when a horse is being ridden is called a saddle blanket. They do not cover the horse's entire body, though a hybrid design that is a cross between a saddle blanket and a horse blanket, called a quarter sheet, is a blanket placed under the saddle but which covers the horse from shoulder to hip while riding. Quarter sheets are sometimes used in cold weather to keep a horse's muscled loosened up when warming up for competition, or on horses that may have to stand around when under saddle and run the risk of stiffening up if their muscles get chilled.