Nanoparticle colloidosomes, whose release can be switched on and off in response to a temperature change, are fabricated. Unlike in other systems, the switchable release does not require the colloidosome shell to deform; it instead occurs due to the adsorption or desorption of a block copolymer, dissolved in the core, at the inner surface of the colloidosome shell, concomitantly blocking or unblocking the pores in the shell. The colloidosomes are prepared using double emulsion templates produced by microfluidics, and are thus highly monodisperse; moreover, they are mechanically stable and consist of biocompatible components, making them suitable for the encapsulation, delivery, and release of a broad range of active materials.