I previously owned the child's size tri-core pillow but after more than five years, it's shot. I wanted something a little bigger, but the label on the pillow doesn't identify which one it is. After measuring, I determined that I had the child's size or petite pillow, and decided on the larger mid-core pillow. I had not idea which firmness I had, because again it is not marked on the pillow. So I went with the standard. It looked great and fit my pillowcase better than the child's size. But when I went to try it out that night, the pillow was so firm I couldn't get comfortable. It seemed to cut off circulation to the back of my head near my neck. My husband got the full-sized pillow and didn't care for it, so we are returning both. I will get the softer, gentle mid-core this time and hope for a better outcome.