From a chemical perspective, polymers are materials composed of numerous molecular chains, either synthetic or natural. Synthetic polymers, including plastics, are among the most prevalent environmental contaminants due to their durability and widespread use. However, recycling plastics can be both profitable and sustainable, as they are inexpensive, lightweight, and abundant. This research paper compares the design and fabrication of building blocks using recycled polymer materials, employing two fabrication methods: a traditional mold/press process and 3D printing with varying infill percentages. A simple building block was designed, and three prototypes were fabricated and tested. The first prototype was fabricated by compressing pulverized waste PET (polyethylene terephthalate) material into molded sheets using hit press machine, which were then laser-cut into precise dimensions and manually assembled into a brick. This method resulted in low structural strength and required extensive production time. The second prototype, produced via 3D printing, demonstrated improved performance but exhibited some structural deficiencies. The third prototype, also 3D printed with 90% infill, exhibited the highest structural integrity in press tests but required significantly longer production times due to increased weight and material usage. The findings underscore the need for optimization through numerical simulation techniques, such as finite element analysis, to enhance the performance and efficiency of recycled polymer composites. This study highlights the potential of integrating recycled plastics into sustainable construction practices, addressing both environmental and structural engineering challenges.