Both in conduction and radiative transfer, the matter is involved in the transfer process, but in a sense it also gets in the way. We can see from this that the transfer process is actually more efficient when there is less matter around. The amount of power a surface can radiate depends on the surface area, its emissivity and its temperature. As conduction, its effectiveness depends on the prevailing physical conditions. However we can say that in the vacuum of space it is the only method of transferring heat and therefore is the most effective in that case.
Convection is fundamentally different from the other two modes of energy transfer.
It results from the bulk motion of material together with its energy content, rather than from passing the energy from one agent to another. As an example, if we want to shift a pile of bricks from one place to another we could form a line of people and pass the bricks one by one along the line. Alternatively we could put them all in a barrow and transfer them in one fell swoop. Whereas conductive and radiative transfer of energy always take place, this is not so for convection. We should accept at this stage that convection occurs only when certain criterion are satisfied.