Insulation Experiment

Why will insulators affect how long a test tube of hot water stays hot?
Background Information
I know that there are many different ways of insulating this test tube, shiny foil can be used because it's a poor emitter of radiation and it will reflect escaping heat by reflecting, because this method is used in flasks to keep hot drinks warm. Though it is a good conductor so will lose heat through to surfaces its touching but it shouldn't matter because it will be touching air and glass which both are really poor conductors. Bubble wrap, foaming and cotton wool can be used as an insulator…