This study reports aerodynamic properties of two runback ice shapes molded from a mid-span full scale B737 aerofoil leading edge together with a series of simplistic ice shapes of the type sometimes used by aircraft manufacturers to mimic performance loss due to runback ice. The runback ice shapes were taken from a study of runback ice growth which had produced flexible silicone rubber moulds. These moulds were used to produce ice shapes without curvature which, together with the “simplistic” shapes were mounted on flat plates and installed into the Cranfield University 8 by 6 foot wind tunnel. A boundary layer suction system was used to match the wall conditions more closely to what would be anticipated on a real aerofoil. The icing conditions approximate to a hold case with the two shapes representing a 4 and a 10 mm thick runback shape. The aerodynamic tests have been performed with a tunnel speed of 45 m/s. Rakes of pitot tubes were used in various downstream locations to probe the flow field. The aerodynamic data is presented in the form of boundary layer thickness and boundary layer displacement thickness measurements. The results show that the popular triangular simplistic ice shape causes significantly more disruption to the flow than the corresponding molded ice shape. The boundary layer thickness and boundary layer displacement values for the 4 mm thick ice shape was best approximated in these tests a band of 1 mm ballontini. For the 10 mm thick ice shape, the boundary layer results were best matched by 10 mm thick rounded off rectangle covered in 1 mm ballontini.