Honestly, that depends on the climate zone you live in. The Building Code of Australia measures the effectiveness of the insulation material depending on its R-value. The higher the value, the stronger is the resistance to heat flow and reduces the burden on your heating and cooling system.
At Just Rite Store, you can find a broad range of insulations for walls, ceilings and under the floor. For Australian homes, we would recommend R4 ceiling insulation to regulate the indoor temperature in all seasons.