RE: Homemade Thermos
Get a small box that is just a bit larger than your soup container. Wrap the soup container with aluminum foil with the shiny side in (facing the container) and place the container inside the box. Add Styrofoam packing peanuts to fill in the empty spaces that surround the container. Styrofoam is a pretty good insulator; it should help to retain heat in the soup. The aluminum foil’s shiny side will help to reflect the radiant heat released by the hot soup back into the container. I have always been a hoarder of packing materials and small boxes and pick them up at work from the trash heap. These items usually lurk near trash cans behind stores, if you don’t have access to them at a place of work. Another method would be to use expanding foam to fill the empty spaces between the box and the soup container. See this website for a DIY project where a guy made a homemade thermal carafe: http://www.thinkythings.org/carafe/build.html You could use another bowl that is larger than your soup bowl for the outside container
via Homemade Thermos.