What materials should I build my calorimeter out of?

I'm building a calorimeter. Obviously the "shell" of the calorimeter is built with an insulator, as to minimize the loss of heat to the environment. This part isn't as obvious to me: when I build the container that the sample will be put in (the container will be submerged in water), should I make it out of an insulator or conductor? At first I assumed that it would be an insulator, but then it wouldn't heat the water up as the sample burns. Thank you!

An insulator is a material that does not allow a trasfer of heat and electricity so using an insulator means no heat will be trasferred . When you are using an insulated material as the body of the bomb calorimeter it means you will prevent heat flow from the calorimeter to the surroundings.

But you should not use an insulator for the container in which u r placing the reactant becuase when the combusiton reaction takes place then the heat has to flow from here to the bomb container carrying the  water .

Another reason for the water staying at the constant temperature could be that the sample probably is not producing enough heat to raise the given aount of water  remember that water has a high specific heat .