A student investigated how the number of layers of cardboard insulation affects the rate of cooling of a beaker of hot water.

They used the following method:

1. Wrap 1 layer of cardboard around a glass beaker.
2. Pour 150 cm³ of hot water into the beaker.
3. Measure the initial temperature of the water.
4. Start a stopwatch and record the final temperature of the water after 10 minutes.
5. Repeat the steps using 2 layers and then 3 layers of cardboard.

State two improvements the student could make to this investigation to obtain more accurate and reliable data.