Research on the use of waste polymeric materials is one of the solutions for developing environmentally friendly recycling processes for steelmaking. Different polymeric materials [i.e., rubber, high-density polyethylene (HDPE), polyethylene therephtalate (PET), and Bakelite], which have different chemical structures and compositions, were selected for this study as carbon resources. The rapid heating to high temperatures provided during steelmaking will break down the polymeric chains and reactions with liquid slag, enabling gas formation. The dynamic changes in the volume of the slag droplet while in contact with the coke/polymer substrates are measured. Significant levels of gas generation and entrapment are present, leading to an improved performance over coke. Carbon/metal reactions were studied by measuring carbon and sulfur pick-up by liquid metal as well as the formation of reaction products at the metal/carbon interface. The measured carbon pick-up value after 2 min of reaction for metallurgical coke was approximately 0.08 wt %, whereas 100% polymers, such as PET and HDPE, showed an increased value of >2 wt %. The proportion of sulfur pick-up was very similar. The formation of interfacial products, in the case of Bakelite–coke blends, was studied, and the presence of CaCO3 used as a filler was seen to influence the chemical properties of the carbonaceous substrate. This study has established fundamentals of the interaction of waste polymers with slag and metal in the steelmaking process.