Twin roll casting can be used to produce aluminium sheet (10 to 0.5 mm thick) directly from the melt. Various defects arise during casting which limit the range of operating conditions suitable for commercial use. A range of casting conditions has been investigated producing aluminium alloys sheet 1.5 to 5 mm thick. Internal and surface defects have been studied. Despite reasonable surface quality and microstructure the high productivity strip showed an abundance of surface bleeds as well as centre segregates. Various techniques have been used to investigate the composition, distribution and identity of the different phases contained within the defects.