This research investigates the effect of heterogeneity in slabs of aluminum, stainless steel, and polyethylene on photon and neutron transmission. This work considers whether novel, heterogeneous combinations of these materials provides improved photon shielding (for metal-infiltrated polyethylene) or neutron shielding (for polyethylene-infiltrated metal). Often, layers of a hydrogenous material such as polyethylene must be combined with layers of a higher-atomic-number material to provide shielding for both photons and neutrons. Several heterogeneous shield configurations are studied in which slabs of a base material are implanted with metal stud arrays ranging from 5 × 5 × 5 to 11 × 11 × 11 arrays. For metal slabs infiltrated with polyethylene studs, it is found that the performance of the heterogeneous slabs as neutron shields relative to the homogeneous material is source-energy dependent. This is a larger concern for polyethylene-infiltrated aluminum (PA) than it is for polyethylene-infiltrated stainless steel (PS) as introduction of these studs impairs PA’s performance as a photon shield (relative to solid aluminum) more than it does for PS relative to solid stainless steel. For polyethylene slabs infiltrated with aluminum or stainless steel studs, it is found that introduction of a sufficiently spaced array of metal studs with a moderate-to-high photon absorption cross section will improve the photon-shielding properties of the shield without impairing the neutron-shielding properties. Use of an insufficiently opaque material or insufficiently wide spacing of the studs will impair the photon-shielding properties, thus making it a less effective shield than homogeneous polyethylene alone. This is a larger concern for PA than it is for PS. This research demonstrates that heterogeneity is more beneficial for stainless steel shields than it is for heterogeneous aluminum shields relative to homogeneous slabs of those materials.