<p>Formaldehyde emissions from medium-density fiberboard (MDF) are significantly influenced by humidity. However, existing emission models predominantly rely on static humidity or instantaneous equilibration assumptions, thereby neglecting the effects of dynamic moisture transfer. This study investigated the impact of moisture transfer on formaldehyde emissions using a combined experimental and modeling approach. MDF samples were exposed to equilibrium and moisture transfer conditions in controlled chambers, respectively. Key emission parameters—initial emittable concentration (<i>C</i>₀), diffusion coefficient (<i>D</i>_m), and partition coefficient (<i>K</i>)—were regressed based on dynamic measurement data. The results indicated that humidity had a positive correlation with formaldehyde emissions, increasing <i>C</i>₀ values more significantly compared to other emission parameters. Moisture transfer introduced directional biases in parameter estimation: inward transfer (from environment to material) reduced <i>D</i>_m by 61% but increased <i>C</i>₀ by 136%, whereas outward transfer (from material to environment) elevated <i>D</i>_m by 40% and decreased <i>C</i>₀ by 13%. These deviations substantially distorted indoor formaldehyde predictions, with simulations underestimating peak concentrations by 6% for inward transfer scenario and overestimating them by 20% for outward transfer scenario. The findings emphasize the necessity of incorporating transient humidity gradients into emission models to improve the accuracy of indoor air quality assessments.</p>