I have a slender cat who weighs around 9 pounds. Therefore, I ordered this pillow in small - but it's too small! I should have sized up but in the product information section,  they said the small size would fit my cat based on her size. Since she can't fit into it comfortably, she's not using it. I'll probably end up giving it away to someone with a tea cup sized dog as I can't be bothered to return it and pay for shipping. Very disappointed because I thought my cat would love this Ball pillow! Update: I gave this to a friend and her cat LOVES it and took to it right away! This is not unusable; we buy items for our felines just KNOWING they will love it only to find they are not interested at all! I'm glad my friend's feline spent many hours enjoying/snuggled up, fast asleep in her Plush Ball Pet Pillow; he was an older cat who was ailing, so I hope his last hours were spent in his Plush Ball Pet Pillow!