向性聚丙烯胶膜:英文是向性聚丙烯胶膜的缩写。它防水、柔韧和极之透明，是一般书套所采用的裱胶材料。

• Opp film: OPP is the abbreviation for Oriented polypropylene. It is water-proof, flexible and highly transparent, and is a type of plastic film commonly used for book-jacket lamination.