AbstractPassive energy‐conversion devices based on water uptake and evaporation offer a robust and cost‐effective alternative in a wide variety of applications. This work introduces a new research avenue in the design of passive devices by replacing traditional porous materials with rigid capillary layers engraved with optimized V‐shaped grooves. The concept is tested using aluminum sheets, which are machined by femtosecond laser and covered by silica or functionalized by oxygen plasma to achieve stable long‐term capillary properties. The durability of the proposed material is experimentally evaluated when functioning with aqueous salt concentrations: both the coated and functionalized specimens exhibit stable wettability after being immersed in saltwater for all the duration of the experiments (≈250 h in this work). The proposed new class of materials is envisaged for use in passive solar or thermal energy‐conversion devices. As a case study, a time‐discretized capillary model is coupled with a validated lumped‐parameters heat and mass transfer model, aiming to estimate the maximum size and productivity of a passive solar distiller employing porous materials of known thermal and capillary properties. This study paves the way to the use of a new class of rigid, highly thermally conductive materials that can significantly improve the performance of passive devices by simplifying the assembly of multistage setups, thus helping to extend their use to real‐scale applications.