Abstract: A system for introducing a flowable additive (3) from a capsule (1) to paint (4), varnish, woodstain or the like in a closed (preferably lidded) container (2) (for example a paint container) modified by the provision of a relatively easily openable inlet (9) into the container. Preferably the inlet is located in a lid (6). The Capsule comprises a chamber (23) which defines a volume which contains the additive. The system is provided with means (25 and 34) for creating an opening in the chamber which can communicate with the inlet and means (preferably a compressible chamber) for positively expelling additive through the opening by contracting the volume which contains the additive. The capsule and container are also provided with co-operable locating means (10 and 30 with 25) which can co-operate to assist in locating the opening created in the chamber in communication with the inlet. Also a capsule and a closed container for use in the system and a method of introducing additive using the system.