What additive is used to improve the flexibility of polymers?

Plasticisers are additives specifically used to enhance the flexibility of polymers. They work by embedding themselves between the polymer chains, which increases the distance between them. This action helps reduce the intermolecular forces that hold the chains together, making it easier for them to move relative to one another. As a result, the resulting material becomes more pliable and less brittle, which is particularly beneficial in applications requiring flexibility, such as in the production of films or rubber materials.

In contrast, stabilisers are used to enhance the longevity of polymers by preventing degradation due to exposure to heat, light, or oxygen. Fillers are employed to reduce costs and improve certain physical properties, such as strength or stiffness, rather than flexibility. Flame retardants are additives that help inhibit combustion and are not aimed at altering the flexibility of the material. Hence, plasticisers are the appropriate choice when the goal is to improve the flexibility of polymers.