Our 40lb princess is very comfortable! I bought the large and it fits her body size pretty perfectly. It also fits perfectly inside of her crate, which is 22x30 for reference. As others have stated, the inner material is chunks of memory foam, but since our dogs favorite thing is our giant bean bag chair, shes okay with it! But if you are looking for solid memory foam, closer to a mattress, this wouldnt be for you.