A poly(neopentyl methacrylate) (p(npMA)) layer was deposited using initiated chemical vapor deposition and its affinity toward gaseous toluene was characterized by Quartz crystal microbalance. High partition coefficients were measured and showed dependence with toluene concentration. In order to better understand these partition coefficient values and evolution, Langmuir adsorption theory was used. Analytical expressions were first compared to experimental data to provide interpretation of the thin film affinity and time response toward toluene. Numerical simulations were realized to take into account toluene mass transport and verify assumptions leading to analytical expressions. Finally, these simulations were used to refine interpretation of p(npMA)–toluene interaction. Analytical and numerical solutions showed good agreement with experimental data, providing an interpretation of toluene with an organic polymer in terms of affinity and also time response.