A delivery system containing an active agent within a polymeric material formed from a thermoplastic composition is provided. Through selective control over the particular nature of the thermoplastic composition, as well as the manner in which it is formed, the present inventors have discovered that a porous network can be created that contains a plurality of micropores and nanopores. The ability to create such a multimodal pore size distribution can allow the delivery rate of an active agent to be tailored for a particular use.