For a given bias across the metal superconducting interface the electrons from the metal enters into the superconductor by forming pairs. Since the metal has the equal number of both spin up and spin down density of states, the spin up electron forms a pair with spin down electron and enters into the superconducting condensate states as super-currents leaving behind a hole in the spin down density of states ( apart from the normal hole in the spin up states). As a result the conduction due to the conventional current (due to holes) doubles at the interface. The extra current that is caused by the extra holes reflected from the interface is called as the Andreev reflection. The amount of reflection depends of the Fermi velocity mismatch between the metal and the superconductor. For a ferromagent superconducting case, the electrons cannot enter into the superconductor because of the absence of the spin down density of states. The electrons get accumulated at the interface and the coefficient of Andreev reflection becomes zero which can be seen as the drop in the conductance below delta, this gives rise to 100% spinpolarization.