The present invention relates to a microcapsule exhibiting desirable sustained-release properties, which microcapsule comprises a core material comprising an active ingredient encapsulated within a silica shell, characterized in that the outer surface of such silica shell has a layer of a metal selected from Group 2a, Group 8, Group 2b or Group 3a of the Periodic Table bound thereto. In other aspects this invention relates to a method of making such a microcapsule; a pesticidal composition comprising microcapsules comprising a pesticidal active ingredient and a suitable carrier; and to a method of controlling pests comprising applying an effective amount of such a pesticidal composition to a locus where pests are or are expected to be present.