This guide is intended to provide readers with a comprehensive comparison of six commonly used thermoplastic materials for injection molding: PP, PE, PET, PA, PC, and PS. From definitions, mechanical properties, and application scenarios to the impact on finished product performance, we aim to help decision-makers across industrial molding corporation, injection mold inc, moulding maker, and other sectors select the optimal material. Real-world use cases in custom plastic parts, plastic parts manufacturing, medical device injection molding, and automotive injection are included to support informed, practical decisions.