I don't think that's the intended use for them. Plus, their hair is designed for natural protection from the elements. When you are cold, the hair on your body stands up. Same with animals. If you put a blanket (or neck sweat) on a horse with a full unshaved coat of hair, you will flatten it down and make them colder as you have interferred with the insulating space of air in the hair.
Sell your sweat on eBay if you don't show or save it for show season when your horse is clipped. Really, I don't even use them and I show my horses.... they are by no means a necessity...
Andrea