<p>A frequently observed yet poorly explained phenomenon in the study of superhydrophobic surfaces (SHS) is that their measured slip length—a key parameter for drag reduction—appears to increase with the Reynolds number in some experiments. The physical origin of this trend has remained ambiguous, limiting our ability to design and optimize these surfaces. This study was designed to resolve this fundamental ambiguity through a combined approach of experimental analysis and targeted computational fluid dynamics (CFD). We first fabricated a durable, porous superhydrophobic coating on a flexible fibrous substrate. This coating exhibited excellent water repellency, with a high static contact angle of 164.6° and a low sliding angle of 4.3°, confirming a stable, air-trapping Cassie-Baxter state. Drag reduction experiments in a laminar channel flow demonstrated the coating’s effectiveness, showing a significant drag reduction ranging from 5 to 25% across a Reynolds number range of 40 to 500. This performance was correlated with a measured increase in the apparent slip length. To uncover the underlying physics, we developed a CFD model. Simulations for a static air–water interface showed slip length&#xa0;decreases&#xa0;with Reynolds number, contradicting our experiments. This paradox revealed that in our experiments the interface is dynamic. Increased flow rate lowers hydrostatic pressure, causing the interface to recede into the porous coating. This recession expands the shear-free area, increasing the effective slip length. Thus, the observed trend is not a direct shear effect but a&#xa0;pressure-dependent phenomenon&#xa0;governed by interface dynamics. This new mechanism is crucial for designing effective drag-reducing surfaces.</p> Graphical abstract <p>From fabrication to flow: Experimental and CFD analysis of drag reduction on porous superhydrophobic surfaces</p> <p></p>