Dispensing closure for mixing the contents of two vessels.

A dispensing closure for a vessel comprising a chamber , a vessel interface and an openable barrier intermediate the chamber and the interface, the vessel interface configured for insertion on to a vessel, and comprising a cam mechanism and a hinge arranged such that by virtue of relative movement of the chamber and a vessel, in use, the cam mechanism opens the barrier and permits material held within the chamber to be dispensed into a vessel. The barrier may include an elongate support structure and a closure cap.