Inner Flap

Inner Flap is a professional term in carton packaging structure, referring to the folded cardboard part inside the outer flap and connected to the box body, usually located on the inner side of the carton opening, used to enhance sealing strength, prevent dust and moisture, and protect the contents. In foreign trade business, this term is commonly found in packaging specifications, purchase orders, letters of credit, and quality inspection clauses. Usage scenarios include: when customers specify carton structure, they require 'the inner flap length must reach more than 2/3 of the box width', or during inspection, check whether the inner flap affects automatic sealing machine operation. Notes: If the inner flap is too short, sealing will not be firm; if too long, it may overlap and push against the outer flap, affecting box flatness; the difference from 'Outer Flap' is that the outer flap is the outermost folded piece of the carton, directly bearing tape adhesion, while the inner flap is folded inward first, providing support and cushioning. In addition, the inner flap does not directly participate in printing and brand display, but improper design can reduce the overall compressive strength of the box. Foreign trade practitioners need to specify in the contract the dimensional tolerance, material grammage, and folding direction of the inner flap to avoid rejection or claims due to packaging non-compliance.