Horse sheets are basically used to keep flies from irritating the horse, and these are known as fly sheets for horses. They should not be confused with fly sheets as used on tents for camping. Neither should they be confused with horse blankets, which are much heavier. Arguably, horse sheets are even more useful than horse blankets as they are lighter. This makes them easier to handle as well. There are different sizes too, including the horse quarter sheet. Many of them are waterproof and these are called rain sheets for horses.
When ordering a horse fly sheet online, you should measure your horse from withers to tail and also the circumference of the horse's saddle fit. It is easy to order horse bed sheets and the like online, as there are specialist stores that offer these. What is more, these can be custom made to include your initials or the horse's or stable's name.
You should look at imported horse fly sheets as well as ones that are locally produced. Some of the finest horse sheets are made in the UK and Ireland. There are also cheap ranges coming out of China and Korea, and these are more than good enough for everyday use for domestic horses. Racing stables and the like might want to look at the imported type. A horse rain sheet is incredibly handy, because it keeps the horse dry and is not too heavy to take off the horse when it is wet. Be sure to look at horse rain sheets when shopping for tack.