I own two of these in different sizes for different ponies and they work great to keep ponies clean and/or protect braids from rubbing. The zipper makes for easy on/off. For size reference....our medium pony is in a small and our large pony is in a medium (could fit in the small, but it was a bit too snug).

I have a large pony who weighs about 800 lbs. The small size was perfect. It fits nice a snug around the ears and eyes. I love that it is not flimsy and really well made. I use it mainly to keep his braids in tack and have used it under winter blankets. I have purchased several of these for my horses and I have never been disappointed with the fit or the quality.