Choose the Rectangular Pet Bed if your dog stretches out to sleep. (If your pup curls up, The Round Pet Bed will be perfect!) ABOUT OUR INSERT: Our new insert is filled with recycled foam in bigger chunks, making it loftier and more cushioning, easier for pets to move around on – and to create the perfect comfy nest. The shell is 100% polypropylene, a fiber so tough that it's often used in outdoor products like rugs. This allows the shell to be much thinner and lighter than the former cotton shell. (Yes, it’s thin enough to be translucent, but that’s the beauty of this fabric: it doesn’t need to be heavy to be dependably tough.) Pet Bed Insert: Small 20W X 28L X 4 1/2H Medium 28W X 41L X 4 1/2 Large 35W X 48 L X 4 1/2H Extra Large 39W X 56 W X 4 1/2H