Citation: BrickNerd - Will Hafner, Overmolding & Dual Molding: What’s the Difference? (Article), January 6, 2022.

... an overmolded piece is exactly what it sounds like—part of the element is molded on top of another part, trapping one of the pieces within another and making a single element with two or more colors. There is a distinct line where one color ends and another begins, and yet, it’s all in the same piece.

... [a] different molding strategy, known as dual molding ... when a mold has rubber or plastic in multiple colors and is injected into the mold at the same time, creating a marbled effect.

Overmoulding requires two moulds, resulting in a clean line between the two colors. Dual moulding involves a single mould with multiple colors injected at the same time into different parts of the mould.