Spherical mesoporous silica particles prepared by evaporation induced self assembly (EISA) were used as templates to form Pt nanowires. Transmission electron microscope (TEM) images of these aerosol-derived silica particles reveal hexagonally ordered pores coiled within each particle, with no obvious termination of the pores on the external surface. Near the particle surface the pores are seen to run parallel to the surface, consistent with the external constraint of spherical geometry. For MCM-41 type mesoporous materials, the pores are straight and accessible at either end for pore filling, but for spherical silica particles prepared by EISA, the pores are not open to the external surface. Hence it is remarkable that Pt nanowires can be formed within the closed pores inside these spherical silica particles, where conventional mechanisms of pore filling would not be expected to be operative. These results suggest that the silica walls in these mesoporous silica allow transport of volatile Pt complexes during wet reduction in H-2. The permeability to gases makes these spherical silica particles especially suitable for gas phase catalytic reactions, while at the same time confining metallic particles within the silica pores.