A fly rug is used on the horse to protect it from annoying insects such as flies, horseflies and mosquitoes. It is mainly used during the warm months of the year when insect populations are at their highest. This typically includes the spring and summer months when temperatures rise and insect activity increases.

A fly blanket should ideally be light in color to deter mosquitoes and flies. Light colors like beige or gray reflect sunlight instead of absorbing it. Since insects are often attracted to dark colors, a light-colored fly sheet can help ensure they bother the horse less.

A pure cotton mesh is better for the horse than a synthetic material for several reasons: Cotton is breathable and allows good air circulation, which helps the horse not sweat easily underneath. Cotton is also softer and less irritating to the horse's skin compared to some synthetic materials. In addition, cotton is better at absorbing and wicking away moisture, which is helpful when the horse sweats or when it rains for a short period of time.