I personally have never had a problem with them - my goats don't nibble and other well known herds that have invested in coats from me, have also not reported this as a problem
They are waterproof and windproof. The outer shell is exactly the same material that is used for horse outdoor rugs so is very tough.
Go to my website - if you haven't already - and check out the pics there. You can call me on 01647 231456 to discuss - evenings best.