Not concrete and both tables cracked in 10+ places after only two months' use (with no exposure to freezing temperatures).  Wish I had more carefully read other reviews that describe bubbling and cracking, plus the actual material.  Joss&Main / Wayfair refused to rectify, but instead suggested that I buy product insurance for every item...in other words, "We don't stand behind our failing products nor do we practice accuracy in our product descriptions."