Ternary composites have been prepared via simultaneous melt extrusion of polyethylene (PE), polyamide-6 (PA6) and short glass fibres in a twin screw extruder. If the fibres are compatible with PA6 a network of fibres welded by domains of the minor PA6 phase is build within the matrix (PE) during the processing. Although a small amount of PA6 is added, the presence of the fibres promotes the continuity of this phase. Thus, the ternary mixture resembles the morphology of a co-continuous binary blend. In this paper the stability of the ternary composites upon annealing at temperatures above the melting of PA6 is studied. An increase of the dynamic tensile modulus is observed. Contrary to the behaviour of co-continuous binary blends, for which the properties often deteriorate due to morphology coarsening, in the ternary composites, it leads to the creation of stronger contacts between the fibres and better mechanical performance. This behaviour is accounted for by a recently developed mechanical model. (c) 2007 Elsevier Ltd. All rights reserved.