When selecting plastic film, you must prioritize material composition (e.g., LDPE, LLDPE, PET, or PVC) as it dictates barrier properties. Key metrics include thickness (measured in microns or mils), where a consistency tolerance of ±3% is standard for high-quality production. Additionally, evaluate tensile strength and elongation at break to ensure the film can withstand mechanical stress during packaging or application. For specialized uses, verify the Oxygen Transmission Rate (OTR) and Water Vapor Transmission Rate (WVTR) to guarantee product shelf-life.