Objects with a fine-scale design of bimetallic beams can display negative thermal expansion. Based on a unit cell design for a negative expansion, produced by Optimal Design methods, we fabricate a thermoelastic "artificial material" using coextrusion of iron and nickel oxides, followed by reductive sintering. A bulk sample with 162 unit cells from Fe-60Ni and Fe-36Ni alloys displayed a thermal expansion coefficient of -3.0 x 10(-6)/degreesC, in agreement with the optimal design prediction. (C) 2004 Kluwer Academic Publishers.