<p>Compared with traditional single-decker bearings, double-decker ball bearings exhibit advantages such as higher limiting rotational speed and longer service life. However, the additional bearing stage inevitably increases the overall mass, which restricts their application in weight-sensitive fields such as aerospace. To address this issue, this study proposes a bionic design for one of the key components of the double-decker ball bearing-the adapter ring. Inspired by the three-dimensional network structure of loofah sponge, characterized by its extremely low specific density and high mechanical strength, a loofah-inspired adapter ring structure has been developed. A finite element static analysis model for the loofah-inspired double-decker ball bearing was established to perform strength analysis on various adapter ring configurations. Furthermore, the mechanical behavior of the bearing under compressive load was theoretically analyzed, and the energy transfer mechanisms in this process was elucidated. Different adapter ring structures were fabricated using additive manufacturing technology, and experimental validation was conducted. By comparing the results of multiple experimental groups, the optimal adapter ring configuration for the double-decker ball bearing was determined. Optimization results indicate that, in the case study, the mass of the adapter ring was reduced by 25.97% and the maximum equivalent stress decreased by 7.74% compared with the unoptimized design. The proposed design approach provides a theoretical foundation for subsequent structural optimization of double-decker ball bearings and their application in lightweight-demanding scenarios such as aerospace.</p>