- Home
- Packaging glossary
- Bag flap
Bag flap
Also known as: flap, bag lip, fold-over flap, closure flap, header flap
A bag flap is the extra strip of film above the bag mouth that folds over to close it and usually carries the adhesive strip.
A bag flap is the extra section of film that extends above the mouth of a bag and folds over to close it. On OPP bags it usually carries the resealable adhesive strip or a permanent shipping seal.
Typical size
On standard clear bags the flap is commonly about 3–5 cm. Small stationery bags work with a short flap, while bulky garments and mailers benefit from a longer one that tolerates bulging contents.
How bag sizes are written
Flap bags are usually specified as width × length + flap. For example, "20 × 30 + 4 cm" means a 20 cm wide bag with 30 cm of usable length from the bottom to the mouth, plus a 4 cm flap. Some suppliers quote length including the flap, so confirm the convention when you order. See pouch dimensions for general sizing logic.
Sizing tips
Measure the product flat, add allowance for thickness and a little clearance for easy insertion, and state whether the adhesive sits on the flap or on the bag body. On hanging bags, the header with the hang hole is a separate area and is not the flap.
Frequently asked
What does "+4" mean in a bag size like 20 × 30 + 4?
It usually refers to a 4 cm flap above the mouth, in addition to the 20 cm width and 30 cm length.
Is the flap included in the bag length?
Usually not, but conventions vary between suppliers, so confirm before ordering.
Related terms
Let's choose your packaging together
Work out the price for your size now, or ask our team which structure suits your product.