Thermoplastic elastomers (TPEs) are conventionally made of block copolymers or partly cross-linked polymer blends. Alternatively, TPEs can be prepared from structured latices, too. Hard-soft latex particles with a thermoplastic core and an elastomeric shell yield highly extendable elastic films, the strength of which depends sensitively on the relative core size and the particle architecture. Core-shell particles were prepared, by two-step emulsion polymerization, with the thermoplastic polystyrene (PS) in the core and the elastomer polyethylacrylate (PEA) in the shell. PEA particles were synthesized first. The PS cores were then incorporated in them in the second step. This method permits the design of monocore. as well as multicore, particles. These PS-PEA particles were not cross-linked in the core or in the shell. They can be classified as microblends. Compression-molded films of them exhibited, therefore, a coarsened microphase morphology that was, however, still much finer than that of simple melt-mixed blends PS/PEA. The film morphologies of monocore and multicore particles were different as far as the former yielded spherical PS domains, while the latter yielded extended PS clusters. This was strongly reflected by the stress-strain behavior: Films from multicore particles responded in a viscoelastic, rubbery manner, while films from monocore particles behaved like viscous liquids.