We revisit the classical problem of liquid imbibition in a single tube with spatially varying wettability. Starting from the Lucas–Washburn equation, we derive analytical solutions for the imbibition time (crossing time) in systems where wettability alternates between different materials. For ordered arrangements, we demonstrate that the imbibition speed depends non-trivially on the spatial distribution, with the "more hydrophobic-first" configuration being optimal. For disordered systems, where segment lengths follow a Gaussian distribution, we show that the classical Cassie–Baxter contact angle, originally derived for static wetting, fails to predict the dynamics of capillary-driven flow. To address this, we propose a new weighted harmonic averaging method for the contact angle, which accurately describes the viscous crossing time in such heterogeneous systems. The choice between arithmetic (Cassie–Baxter) and harmonic averaging is fundamentally determined by the flow topology. In our single-tube model, the fluid encounters regions of different wettability sequentially and cannot bypass hydrophobic sections. This series arrangement of flow resistances leads naturally to harmonic averaging, analogous to electrical resistors in series. In contrast, the Cassie–Baxter arithmetic averaging would be more appropriate in systems where flow paths are parallel rather than serial, e.g., in interconnected pore networks where fluid can preferentially route through hydrophilic channels. We generalize the theory to systems with an arbitrary number of material components and validate the results numerically. In the talk, we will also discuss ongoing extensions of this work, including relaxing the axial symmetry assumption and the role of contact angle relaxation and pinning effects at material boundaries.