Block copolymers, easily tailor-made by growing poly(ethylene oxide) from a commercial hydroxyl-terminated poly(ethylene-co-butylene) (Kraton liquid), can self-assemble over a wide range of concentrations into mesophases constructed from spherical micelles with small polydispersity. These phases are analyzed in detail by transmission electron microscopy and small-angle X-ray scattering (SAXS) by their silica replicas, hollow negative replicas of those structures made by nanocasting. The influence of polymer concentration on the structural order of the porous silica and the size of the constituting micelles is examined. At high volume fractions, a glasslike, disordered structure is obtained, while close-packed structures with long-range order are found in an intermediate concentration range with high local mobility of the micelles but sufficiently strong intermicellar forces to drive colloidal crystallization.