Day 4: [BACK TO THE DRAWING BOARD]

Even though the top of the thermos wasn't completed and the thermometer was not in place, we decided to start testing anyways to check the durability of the thermos. The thermos was generally able to retain the heat, but the plastic bottle which we had placed inside the 2L bottle was more than 500 mL, which did not meet the requirements because we needed to use 500 mL or less. Trouble-shooting began as more adjustments are being made and further research was being done. Some of the ideas we shared were, to use a Styrofoam cup or coffee cup for the inside of the 2L bottle as they were both small so would probably use less then 500 ml  Luckily enough a plastic bottle was given to us that met the requirements so we started rebuilding using it right away. Another thing we changed besides the bottle was the sock which was switched to a thicker cotton sock because it's a better insulator as it can trap air from being transferred.

(http://wiki.answers.com/Q/Why_cotton_is_a_good_insulator#page2)