NASA will fly x-ray microcalorimeters on several mission payloads scheduled within the next 5 years: New and improved IR/Visible blocking filters are urgently needed to realize the full potential and throughput of these missions. The innovation proposed, high transmission polyimide support mesh, will replace the nickel mesh used in previous blocking filter designs. Polyimide's composition affords high transparency to x-rays, especially above 3 keV. Phase 1 prototypes demonstrated 11-15% higher transmission than comparable nickel mesh across the UV-Visible-NIR range. With development of the Phase 1 process in Phase 2, the mesh will be optimized for strength, transmission, integration with filter materials, and filter lifetime; it will include deicing capability as required. Lithographic production means adaptability to meet future mission-specific filter performance requirements. The Phase 2 project will achieve a flight readiness level of 5-6 for blocking filters using the new mesh. Phase 1 results show that with successful process development, the proposed high transmission polyimide mesh will significantly improve mission throughput and effective area for microcalorimeter payloads on proposed NASA missions such as Spectrum-X-Gamma and NeXT in the near term as well as Constellation-X.