Pink foam board from Home Depot, cut to fit around fireplace. I duck taped it together (underneath as well). Then, I covered it with quilt batting (folded to form layers). Lastly, I got some cheap fabric from hobby lobby and hot glued it underneath.
I wanted a stylish yet practical way to babyproof my fireplace hearth. I measured the hearth then built a frame out of pine to slide over it then used rubber pipe insulation to cushion the corners. I then wrapped it in polyfoam batting to add more cushion then upholstered it using tablecloth fabric that has a clear plastic coating so I can easily wipe it clean when sticky little hands touch it! Voila!