 You've been heating your leftovers the wrong way, never use these. Use these instead. Why? The corners of square Tupperware absorb energy from four directions. The sides get hit from three, while the center only gets energy from two. So the food in the corners gets overcooked, and the food in the middle gets undercooked? Undercooked overcooked. That's why the people that literally make microwaves suggest round containers. All edges get heated from three directions, so the food is heated more evenly. Now, if you value storage space over better reheating, then square is the way to go.