We were wondering which material can keep water warm the longest.
We had a control cup with warm water and no insulation around it. We measured the temperature of the warm water. It started at 55 degrees but dropped to 24 degrees after lunch.
We had 3 other cups. Each of these started with water of the same temperature, but had a cushion of newspaper, plastic or cotton wool around them.
After lunch we took the temperature of all the cups of water. We found that cotton wool kept the water warm for the longest, then newspaper and finally the plastic.
We had all predicted the outcome and we were delighted that most of us had guessed that cotton wool would be the best insulator. It is!