THE nucleation of polymer crystallization by various heterogeneous additives has been studied empirically1–4 some authors have attempted to understand the mechanism of the nucleation process5. In an examination of isotactic polypropylene crystallization on carbon fibres, we showed the importance of substrate geometry on the nucleation of polymer crystallization from the melt6. Here we report further work which confirms that the effectiveness of a heterogeneous nucleant depends on its structure. The novelty of these studies lies in our use of a replication technique to transform “non-active” surfaces into surfaces which readily nucleate crystallization from polymer melts.