A method for producing a structured material for accommodating passage of fluids,
particularly high viscosity fluids, through the structured material. In one embodiment,
the structured material is a composite material formed of a first layer, for example
a polypropylene polymer, having a first shrinkage extent and a second layer bonded
to the first layer, for example an ethylene-propylene copolymer, having a second
shrinkage extent different from the first shrinkage extent. In another embodiment,
a structured heterogenous material is made of a heterogeneous mixture of at least
two homogeneous fiber sets or components having different shrinkage extents.