Wanting to turn this little tin into a fly box, whats the best foam/other material to buy to hold flies?

As the title says, I have this small tin that I would like to turn into a small fly box that i can keep in the car for emergency fishing. Whats the best foam to use? I figured i could find something at Michael's, or would foam for tying flies work? Are there any other materials i might consider? Looking to cut it to size and glue it inside.