Functionally graded ultra-high temperature ceramics containing variable amounts of short carbon fiber were designed to combine and maximize the toughening contributions due to fiber bridging and residual stresses upon layering. Stress fields evaluated by finite element model on (AB)nA and more complex asymmetric architectures were compared to the experimental fracture toughness pointing to an effective toughness increment in those structures where the notch fell in zones of residual compression. For the best composites, toughness at room temperature achieved 7 MPa·m^0.5 and further increased to 10 MPa·m^0.5 when tested at 1500°C within a light ZrB2-based composite with density below 4 g/cm³. Preliminary results upon ablation tests and next manufacture developments are also illustrated.