The design of a film cooled dual-bell nozzle is presented. The nozzle is part of a thrust chamber assembly that adopts an existing LOX/GH2 thrust chamber. The dual-bell base nozzle, including the gaseous hydrogen cooling film injection, is a downscaled redesign of an already tested film cooled TIC nozzle. Future hot flow tests at the test facility P8 will study the impact of a ROF variation and a cooling film mass flow variation on the operation mode transition of the dual-bell. For this reason, a homogeneous hot flow and cooling film distribution are mandatory. To meet those demands, extensive numerical studies were performed and design optimizations were derived. The test specimen will be operated under sea level conditions.