Windsor & Newton Flow Improver is an additive that loosens the surface tension of water within the acrylic film. It increases flow, allowing the artist to apply areas of flat colour evenly without changing the colour strength. The increased flow is also ideal for masking applications (as the colour lays more smoothly and evenly against the taped edge) and for flowing, gestured water colour techniques. Flow improver is also the best medium for “staining” applications. Flow improver should be used only in the amount needed to achieve the desired effect.