This paper deals with the use of a pack aluminization process for the transformation of stainless steel wires and three-dimensional (3-D) interconnected fibres into intermetallic compounds. The decomposition of the pack was first investigated using differential thermal analysis. For both sample geometries, wires and interconnected fibres, the influence of trace amounts of oxygen in the processing atmosphere on intermetallic formation is shown. In a normal furnace atmosphere with Ar-flow, aluminium deposited from the pack on the sample surface but did not diffuse inside because a surface oxidation layer appeared. Upon active limitation of the oxygen partial pressure, Al was able to diffuse into the sample, up to 100 μm after 4 hours at 1000°C for the stainless steel wire, and resulting in complete transformation of the 3-D fibre network.