Thermal rectification has been intensively investigated at the nanoscale. However, it still needs to be explored in order to achieve a high thermal rectification efficiency (TR) in bulk materials. Here we report bulk-scale thermal rectification in bilayered silicon rubber (SR) composites by elastic modulus asymmetry and thermal radiation. The AlN filler concentration in the bottom layer is fixed at 5 vol%, whereas that in the top layer varies from 5 to 51 vol%, achieving elastic modulus asymmetry. The different AlN concentration inevitably changes thermal conductivity and thermal radiation heat transfer of each layer. The TR of SR5–51 vol% with the elastic modulus ratio of 10.9 is as high as 18.4% (ΔT = 60 °C), where the subscript indicates AlN concentration. It further increases to 82.9% (ΔT = 115 °C) when the elastic modulus ratio is increased to 141.8 by constructing SR51 vol% on top of soft graphene oxide sponge. The TR values are considerably smaller when the combined thermal conduction and radiation mode is simulated by finite element method. A three-dimensional lattice vibration model reveals that the elastic modulus asymmetry alone can provide a high TR as an important thermal rectification mechanism.