Pizza boy(delivery man ) keep the Pizzas in a  box which is made up of hard material from outside an inside it is made of thermocol (polystrene (C8H8)n).Thermocol is a poor conductor of heat so, it niether conducts heat energy to the surroundings nor it absorbs heat energy so the pizza kept in the box made up of thermocol will remain hot for a longer time. The box can be made up of any other material also from inside which is a poor conductor of heat.
I hope u got it!