With unprecedented freedom in materials design, additive manufacturing (AM) technologies provide us with the capabilities to leverage from geometric complexity. If properly exploited, this allows us to design performance instead of geometry, where the latter is not user defined but a result of a computer optimization. Entirely new mathematically defined, dimensionally stable carbon materials are presented that shrink isotopically under a pyrolysis process generating complex CAD defined 3D shapes with theoretically two to three orders of magnitude increases in permeability and ohmic conductance over conventional Gas Diffusion Layers. The shown lattices can be structured with resolution in the 10 µm regime having total dimensions over several cm. Initial performance tests in full cell configurations inside a PEMFC are presented. The area of mathematically defined, ordered materials with predictable and optimized performances might shape an entirely research field relevant for low cost and high-performance energy converters.