Ice patterns can be used to make ceramic investment moulds for metal castings. Owing to the characteristics of ice, the ceramic mould must be made at subzero temperatures and consequently, requires a different formulation than shells built at room temperature. Success of this process depends greatly on the fracture toughness of mould materials. The present paper describes the experimental results of fracture toughness of mould materials processed from different compositions. The Taguchi method was used to reduce the trial runs. The parameters considered included the ratio of fibre containing fused silica and aluminosilicate powders, the volume of binder and the volume of catalyst. The microstructure and green fracture surface of test bars were also examined to understand the underlying mechanism. While conducting the four point bend test on ceramic mould samples, some samples had exceedingly low strengths appearing as outliers in the Weibull analysis. Examination of these low strength ceramic samples improved understanding of failure of mould materials. Sound moulds have been made for the investment casting process with ice patterns based on the analysis of experimental results. The casting of an M8 bolt is used to demonstrate that metal castings of complex geometry can be fabricated using ice patterns. The measured tolerances are within the required tolerance range.