In the Lost Foam casting of Al alloys the foamed polystyrene pattern is broken down by the heat of the advancing liquid metal as it fills the mould. This has led to discussion about the possibility of increased hydrogen pick-up by the liquid metal from the gaseous pattern degradation by-products accumulating at the liquid metal-foam pattern interface, leading to detrimental porosity in the final casting. The results presented here were derived from comparisons of the initial measured hydrogen content of the liquid Al alloy before mould filling, and the hydrogen content of the final castings, coupled with real-time X-ray imaging of the filling of the mould to determine whether entrainment of the foam pattern degradation by-products was occurring. This showed that increased hydrogen content in Al Lost Foam castings was attributable to the entrainment of degrading pattern material, and not due to increased absorption of hydrogen from the interfacial atmosphere.