Abstract Biomimetic composites of polymer and clay are known to possess high mechanical strength and excellent barrier properties. However, the ductility of these composites is always low. One way to overcome this limitation consists on the incorporation of plasticizers which work effectively for the pure polymer. It is shown here that an imidazolium-based ionic liquid is a more effective plasticizer for chitosan, in terms of suppression of the glass transition temperature and mechanical properties, than the more commonly used glycerol. This might result from the ionic interaction between both species that is not present when glycerol is used as the plasticizer. Biomimetic composites of chitosan and clay were also prepared containing these two plasticizers. A similar effect on the mechanical properties was observed as for the pure polymer, that is, even at a very low (∼12%) final concentration, the ionic liquid was a better plasticizer than glycerol, being able to double the ductility of the composites. Regarding barrier properties, no difference was observed between the original and the plasticized composites. This study thus shows that the incorporation of plasticizers is an effective method to improve the flexibility of biomimetic composites without deleterious effect on their excellent barrier properties.