dont know specicifics on the table or anything.
Balsa's probably a fair insulator as wood goes, but you might want to line your box with styrofoam, or just use a styrofoam cooler. Additionally, line the interior with material from one of those reflective space blankets- available from camping supply or military stores. Make the container as small as you can, minimizing any free space between the beaker and the walls. It would be awesome if you could pull a vacuum on the system, but that would probably be over-engineering your basic experiment.
You are doing this work you should understand it better. No body else can suggest you bout your job. You are in there and you should no it better.
