I've written about blankets previously on my post... "To Blanket or Not to Blanket"
I recently came across this information and think this is probably the most comprehensive guide I've seen regarding blanketing your horse.
Measure Your Horse
Measure the distance from the center of the horse’s chest (Point A) to the point of the buttocks (Point B). Include the widest part of his shoulder and keep the take measure level. Record this distance in inches. This is your horse’s blanket size.
Learn The Terminology
Turnout Sheet: Lightweight (usually 0g – 100g of fill), waterproof, and securely fit the horse. They provide your horse with some degree of protection against environmental elements (wind, rain, snow, hail) while turned out in the pasture.
Anti-Sweat Sheet: Help keep the horse clean while they cool off after a bath or hard workout. Can be used as an added layer of warmth underneath turnout or stable blankets.
Quarter Sheet: Designed to cover the horse’s hindquarters and wrap up under the saddle flaps or over your legs. They are useful for cool mornings while warming up.
Turnout Blanket: Have an inner layer of fill for warmth, a waterproof outer layer, and has multiple fittings to allow it to stay securely on the horse while they are turned out in the pasture. Many come with a hood or allow for a hood option.
Stable Blanket: Provide your horse with warmth during colder months of the year, worn while they are in their stall; they are not waterproof and do not securely fit the horse. They can be used for additional insulation underneath turnout sheets.
Stable Sheet: Lightweight, snug-fitting layer used to keep your horse’s coat clean while they are in their stall; they are not waterproof and do not securely fit the horse. They can be used for additional insulation underneath turnout sheets. A stable sheet can have a snug fit.
Fly Sheet: Fly sheets are used during summer months to provide your hose with some degree of protection against biting insects. Can be used underneath other sheets or blankets as an added layer of warmth.
Cooler: Coolers are placed on horses after baths or if they are sweating from a hard workout during the winter. Their purpose is to help your horse dry faster while keeping them from getting too cold.
Rain Sheet: Waterproof throw-over sheet which fits over the top of riding tack to protect it and the horse from getting wet. Useful for in-between classes at horse shows.
Parts of A Blanket
Breathable - The level of breathability is determined by how easily air can pass through the fabric. If fabric doesn’t breathe well, mold and mildew can become a problem.
Denier (D) – A unit of measurement that describes the linear mass density of the material; a good measure of strength and durability when comparing two deniers of the same material. The higher the number, the stronger the material.
Polyfill – Synthetic fibers, as polyester, used as filling or insulating material in blankets which gives them warmth. It is measured in GSM (grams per square meter), commonly depicted as ‘g’ in the U.S.
Questions To Consider
Reference: The Complete Guide to Horse Blanketing, Everything You Would Ever Need to Know About Blanketing Your Horse, http://www.horsedvm.com/infographs/horsedvm-complete-guide-blanketing-horse-blanketing.png, Retrieved Nov 24, 2017.