After finding several sizes I then realized I needed to know quantitatively how much heat was moving through the metal. I noted that I could exploit the known properties of water for this purpose. The thermal property I exploited is known as the heat capacity of the material. How much warmer it gets depends dramatically on the material. Wood not only conducts heat slowly it heats up slowly as well.
Metals tend to conduct heat well and they also heat up pretty quickly.
Now water is a handy material which has been extensively studied and its heat capacity is well understood. This meant that by measuring the change in the temperature of the water inside my cans I could determine how much heat had left the water through the can. If I wanted to I could also calculate the thermal conductivity of the metal. I got ridiculous numbers for the thermal conductivity of my metal cans. After some thought I realized that there was another important process taking place that I had not taken into account.