The maximum amount of power allowed through a circuit according to the Australian Electrical Standards is dictated by the following three things; The cable size, temperature rating and insulation environment.

A cable can be deemed to sit in one of three environments. Free air, where the cable is untouched by any insulation. Partially surrounded, the cable touched insulation on one side. Completely surrounded, the cable is completely encased by insulation.

Typically, batts will create a partially surrounded environment for cables and blow-in will create a completely surrounded environment. As a rule of thumb, the more insulation that goes around a cable, the less power can be safely put through the circuit as the insulation reduces its ability to dissipate heat.