Vesicles can be made from various polymers, from modified biological to wholly synthetic, in media ranging from complex to neat organics and water. Although the canonical form of polymers that have the ability to assemble into encapsulating vesicles is an amphiphilic H-P (hydrophobic-polar) diblock, additional block copolymers from triblocks to pentablocks have also been shown to assemble into vesicles. Polydispersity seems to have a minimal effect, but solvent requirements may well depend on the proportion of H to P as well as the molecular weight. What is clear from all of the ultrastructural characterization done on polymer vesicles is that the 'universal' thickness of 3-4 nm, which is well-known for natural lipid vesicles, reflects no physical limitation on the amphiphilic assembly at the nano-scale. Emerging material characterizations emphasize the dominance of the two-dimensional H-P interface and the unnatural robustness possible in the responses of polymer membranes. (C) 2000 Elsevier Science Ltd. All rights reserved.