In this paper the modelling of TRI in hydrogen jet flames is investigated. TRI is modelled using a stochastic methodology similar to Faeth's research group's methodology. The present work differs from Faeths by investigating the predictive capability of the TRI model to the PDF used to generate realisations of the instantaneous mixture fraction field. Two PDFs are considered, a beta PDF and a truncated Gaussian PDF. Surprisingly the predicted heat flux distribution external to the jet flame exhibits sensitivity to the shape of the PDF implemented. This is counter intuitive given previous studies where the predicted flame structure is shown not to be sensitive to the PDF implemented as part of the turbulent combustion model. The sensitivity of the predicted heat flux distribution to the shape of the PDF implemented as part of the TRI model is analysed and the reason for the sensitivity identified. An additional conclusion of this work is the beta PDF gives a more accurate prediction of the heat flux distribution compared to a truncated Gaussian PDF. (C) 2012 Elsevier Ltd. All rights reserved.