I have a dog who has very sensitive skin and is cold natured. I have had many different shirts for him, all with benefits and drawbacks. Fit is a real challenge for my muscular chested, slim-hipped bull dog. This shirt really resolved that problem. Excellent design and very stretchy material makes for a great fit. My dog weighs 65 lbs and I bought X-large. It is a light-weight knit so it does not provide much warmth, but helps some. It does protect him from allergens and scratches when wrestling with his "little sister."