The results of a detailed theoretical examination of laminar natural convection heat flow in a triangular porous cavity with significant radiative heat transfer and porosity variations are presented. Two-dimensional laminar incompressible flow was considered, in which the left slant and right walls were at low and high temperature, respectively, and the remaining (top) wall was adiabatic. The Darcy-Brinkman isotropic model was utilized, and the coupled governing equations were solved by a numerical method utilizing finite differences. Visualization of the isotherms and streamlines was achieved using the method of energy flux vectors (EFVs). The impacts of the different model parameters (the Rayleigh number, Darcy number, porosity, and radiation parameter) on the thermo-fluid characteristics were studied in detail. The computations showed that convective heat transfer was enhanced with an increase in the Darcy number (permeability), which also led to intensification in the density of the EFV patterns. The flow accelerated with an increase in the buoyancy effect (Rayleigh number) and the temperatures also increased with greater radiative flux. The average Nusselt number decreased with higher porosity. The simulations are relevant to hybrid porous media solar collectors. © 2020 by Begell House, Inc. www.begellhouse.com