Barrier dispersion coatings have been used to improve barrier properties of paper-based materials. Like other technologies such as thermoplastic composites, dispersion coatings include fillers to create obstacles that complicate the pathways for permeants through coatings. The development of these technologies has received significant attention where even predictive barrier performance models have been created. However, to the best of our knowledge, none of them are applicable to barrier dispersion coatings. This research proposed a mathematical model to predict the relative permeability of barrier dispersion coatings applied on paper-based materials based on Fick’s law. The uncertainty of the barrier properties due to variation in filler orientation and spatial location was included through Monte Carlo simulation. Model validation against four models previously published by other authors, and water vapor transmission rate measured on three coating formations and two coating thicknesses was also conducted. The model predictions and experimental results showed that the increase in the amount of fillers reduces the relative permeability, and this reduction can be higher if the size of the fillers is larger. The predictions agreed with experimental results particularly at volume fractions below 10%. In most of the cases, the proposed model achieved better prediction in comparison with those already published. The model is useful to predict relative barrier performance of different coating formulations and can be used as a tool for future developments.