The hierarchical morphology of commingled plastic waste in the form of thick beams prepared by the ET-1 process has been examined. Blends of recycled high-density polyethylene (RHDPE, New Jersey Curbside Tailings) with 25 and 35 wt % expanded polystyrene (EPS) were compared with blends of a virgin high-density polyethylene resin (VHDPE). At the macroscale, observed with the optical microscope, the beams consisted of a solid skin that extended about one-third of the distance to the center of the beam and a voided core with about half the density of the skin. The phase morphology of the skin at the microscale was characterized by examining etched cryogenic fracture surfaces in a scanning electron microscope. The blends of RHDPE and VHDPE exhibited a gradient morphology with highly elongated EPS domains near the edge and spherical or co-continuous EPS domains closer to the core. The morphology gradient was created by the competition between the relaxation rate of the melt-flow morphology and the cooling rate in the mold. In addition to high-density polyethylene, a variety of other components were identified in RHDPE by photoacoustic infrared and thermal analysis. These included polypropylene, polystyrene, poly(ethylene terephthalate), and chunks of nonpolymeric material. As a result of the heterogeneous composition, the crystallinity of RHDPE was significantly lower than that of VHDPE.