The key to insulation is to remember the three paths of heat flow:
All different types of insulation work by utilizing one or more of these three principles. The most commonly used method is to create a thermal break by creating an air space between two adjacent areas, Foam, Fiberglass, and straw all work by creating static (dead) air space between two adjacent areas. This reduces heat flow by conduction and convection. The foil seen on many modern manufactured insulations will also reduces heat flow by radiation. To develope an insulator from indeginous material you can use this principle of creating static air space between the areas that will have and/or maintain a temperture difference. Example... an aluminium can with the pop (or zip) top has a static air space within the empty can, by stacking the cans together an effective form of insulation will be created. Other stable materials can also be used in the same manner. Note: The ideas mentioned here are for "insulation" and not for "thermal tempering" which is an entirely different method of temperture control in a structure.
Offered by Ray.