A number of factors can affect the rate of cooling of an object.
These are :
Surface area to volume ratio; number of layers of insulation; type of insulation; colour of object; starting temperature of object.
Any investigation into one of these factors will need to carefully control the others to make sure they do not have an effect on the outcome.
The simplest way to identify how each of these factors affects the cooling is by examining the cooling curve for hot water.
A known volume of hot water should be placed in a container. The experiment should then be set up so that the temperature of the water can be measured at 30 second intervals over 10 minutes.
By plotting these results a cooling curve for those conditions can be obtained.
the experiment can then be repeated, changing one of the variables - for example adding a layer of insulation, or using a different shape container.
By comparing the cooling curves for the different conditions we can see both the overall effect after 10 minutes, and determine how the rate of cooling is affected in each case.