A PETG folding carton window is a film patch in a paperboard structure, and the design question is not the film alone but the margin between the window and the folds that will flex on a filling line.
A cosmetics converter in Milan ran window cartons with the window cut 2 mm from a fold. Cartons split at the fold on the packing line, and the fix was a redesign with an 8 mm margin, not a thicker film.
PETG folding carton film and patch margin
- Small window: 0.25 to 0.3 mm
- Large or rough handling: 0.4 to 0.5 mm
- Window to fold: 8 mm minimum
- Patch overlap onto board: 6 to 8 mm
The margin is structural. Paperboard carries the flex and the film only has to be a window; when the window sits on the fold, the film becomes the hinge and tears at the corner within a few hundred cartons.
Board coating and cold chain
Patch adhesion depends on the board, not the film. A coated board with a compatible lacquer holds a heat-sealed patch for the life of the pack; an uncoated recycled board absorbs adhesive and the patch lifts at the edge.
Cold chain behaviour is worth testing before a launch. A thin film in a chilled cabinet takes up moisture at the edges and curls, which shows on shelf as a window that looks like it is peeling even when the seal is intact.
For food-contact paperwork on the film, see PETG FDA compliance, and for forming behaviour, PETG thermoforming.
Send your carton dieline, fill line speed and product to oversales@rpplexiglass.com for window film pricing.
Frequently Asked Questions
What thickness PETG film for a carton window?
0.25 to 0.3 mm for a small window on a retail carton, 0.4 to 0.5 mm where the window is large or the carton is handled rough. Thicker film resists tearing and holds shape on a shelf.
How is the window patch applied?
By adhesive lamination during carton converting, or by heat sealing to a coated board. The board coating must be compatible, or the patch lifts at the window edge after a few weeks.
Why does a window tear at the corner?
The window cuts too close to a fold line. Keep 8 mm between window edge and fold so the board carries the stress and the film is not asked to act as a hinge.