In recent years wire EDM cutting speeds and final surface roughness have been continuously improving. Much higher cutting speeds during roughing and surface roughness values lower than 0.1 mum Ra during finishing can be obtained. These enhancements are mostly attributed to the use of more advanced generator technology, but also to the type of wire. This paper discusses the use of new composite wires comprising a high tensile core and several coatings. Several wire compositions are introduced and experimentally tested. The use of a very high tensile core, the application of a layer that prevents the process heat from weakening the wire core and the presence of a superficial top coating with different possible functions are discussed. Results obtained while cutting with prototype wires show that a significant rise in accuracy especially in corner cutting is attained, while the cutting rate is at a comparable level as commercial reference wires.