It is round. I have never tried to put a sandwich in it. I use it with rice, soup, and fruit or vegetables or some other sort of leftovers. You could use a bun for your bread or any other round bread (or cut your square bread into a circle). I never really felt like I needed a complex lunch container if I just wanted…

I prefer the Zojirushi Bento Sets. It can keep food warm if it has been heated with water or the individual containers can be microwaved. It even has a watertight container for soups or other liquid dishes. Also, like all Zojirush products, it is insanely easy to clean.