The Lost Foam casting of Al alloys has not yet reached its full potential because of the complexity of the process, and the fact that it is still poorly understood. In this paper, the permeability of typical pattern coatings for the Lost Foam casting of Al was measured, and found to vary from about 0.1 Darcy, (10(-13) m(2)), for a low permeability coating, to about 1 Darcy (10(-12) m(2)), for a high permeability coating. Permeability was reduced by increasing coating thickness, but examination of the coatings on a hot-stage SEM suggested it would be unaffected by increased temperature. The results were used to infer how the filling of a Lost Foam polystyrene pattern could be influenced by the permeability of the pattern coating.