The viscosity of liquid mixtures in e-vapor products (EVPs) is key to their performance and is sensitive to mixture composition and temperature. To date, no accurate model exists for the viscosities of said mixtures. Herein, we report an empirical model for the viscosity of liquid mixtures containing propylene glycol (PG), glycerol (GL), and water (W), representative of the mixtures in EVPs. The model captures the interactions between component liquids and makes accurate viscosity predictions for liquid mixtures of PG, GL, and W, as well as such mixtures containing small amounts of menthol, from 20 to 80 degrees C. The model is calibrated to new experimental data for PG-GL-W ternary mixtures and may be extended to incorporate different or additional liquids or a wider temperature range given additional fitting data. The model should also prove beneficial for food, cosmetic, and pharmaceutical products containing aqueous solutions of PG and GL.