Desiccant composites were prepared from seven high-impact polystyrene copolymers and two homopolymers (polystyrene, PS) to study the effect of structure and elastomer content on their functional and application properties. Composites containing an 4A type zeolite up to 50 vol % were homogenized in an internal mixer and then compression molded to 1 mm thick plates. The water absorption capacity of the composites increases strongly with zeolite, but decreases slightly with increasing polybutadiene content. The overall rate of water adsorption decreases with increasing zeolite content, and it is influenced quite significantly by the amount of elastomer as well. Zeolite and elastomer contents determine both functional and application properties, but structural parameters also play a role. The size of the dispersed butadiene droplets, the amount of PS embedded into them, as well as the encapsulation of the zeolite into the droplets also influence all properties to a smaller or larger extent.