Heterogeneous material properties can be found in new hybrid materials as well as in existing engineering constructions, e.g. dams. The material properties can be modeled by correlated random fields, taking into account their possible interdependencies. The vaguely known random field parameters like correlation coefficient and correlation length are described by fuzzy sets. Applying those fields in a reliability analysis result in failure probability fuzzy sets that can be interpreted by the engineer. This proposed methodology is applied to a simple illustrative one‐dimensional model to show the principle procedure. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)