Insulation is the most important way to reduce heat loss in winter and heat gain in summer. Depending on your home, insulation can be quick to retro fit without major renovations, but should certainly be included in new builds or during major renovations, when it is easier to install.
What is insulation?
All materials allow heat to pass through them. Insulation reduces the amount of heat transferred through building materials like brick, plasterboard, glass and metal by providing substantial resistance to heat flow either in to or out of a building. This means that the need for heating and cooling is minimised. Ideally, insulation should be installed in the ceiling, walls and floors of your home to create a sealed envelope which acts like a thermos in winter to keep heat inside, and like an esky in summer, to keep heat out.