This paper describes the finite element simulation of multilayer injection moulding in an axisymmetric cup-shaped geometry. The residual thickness of the outer material can be investigated at any stage of the filling process. The occurrence of material breakthrough is predicted and physically feasible results are presented for different injection delay times. Tracking of both a free filling and a fluid/fluid front is performed using different techniques. Location of different material positions is governed by point inclusion algorithms. Shear flow instabilities at the fluid/fluid interface are investigated for various core-skin material combinations.