Drying is a core rubber processing step that directly affects product performance. Yet systematic comparisons of mass transfer across drying methods—and the link between moisture migration and microstructure—are lacking. This study compares hot-air and microwave drying of natural rubber, revealing how each governs dehydration kinetics and microstructural evolution. Both methods show three-stage dehydration (rapid, falling, and constant rate), but microwave drying cuts total drying time by over 80% due to volumetric heating. A high-precision Page model (R2 > 0.99) fits both methods well; its exponential parameters capture stage-specific moisture migration. Hot-air drying follows counter-current transfer (heat in, moisture out), yielding low Deff (0.76–6.84 × 10-7 m2/s) and hm (0.08–0.39 × 10-7 m2/s). Microwave drying drives co-directional heat and mass transfer via electromagnetic excitation, giving Deff (2.33–7.47 × 10-6 m2/s) and hm (0.29–1.29 × 10-6 m2/s) ∼10× higher. LF-NMR confirms these molecular-scale differences and establishes a quantitative link between relaxation time and hm—enabling real-time drying monitoring and optimization.
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