In this paper, both experimental trials and numerical simulations are presented to improve our understanding of the heat transfer within granular polymer beds for systems with and without shear. Both amorphous polymer, polystyrene (PS), and a semi-crystalline polymer, high-density polyethylene (HDPE) of varying particle size from 6 mm to 25 mm were examined. The estimated effective thermal conductivity data from the experimental trials was found by fit to two simple semi-empirical models allowing readers to readily approximate the property based on porosity of the bed and solid thermal properties. Discrete particle simulations, i. e. DEM, were used to recognize the importance of heat transport through the stagnant interstitial gas phase in comparison to particle-particle conduction. The results underscore the importance of including an effective thermal conductivity for granular solids in an extruder when using continuum models.