A pouch design can look right on screen and still print differently on clear or metallized film. One reason is that the material behind the ink changes how the colors appear. On a white-coated surface, the printing surface provides a white background. Clear and metallized films behave differently: the artwork has to specify where white ink provides a backing, where the film underneath stays visible, and which areas are left unprinted. This guide covers what to check before you approve artwork for custom Mylar bags.
Those instructions usually sit in the production file as separate print separations, alongside the visible design. They are easy to miss if the approval only looks at the design itself. This guide focuses on three of them: white ink, clear windows and the type of proof used for sign-off. It assumes the pouch size and window position are already settled; if not, start with how to size a Mylar pouch for disposable vape hardware.
Printing methods, laminate structures and prepress requirements vary. Confirm the requirements for your order against the supplier’s approved material specification and artwork instructions.
Why the film changes what the artwork means
Most process inks are partly transparent, so they take some of their appearance from whatever is behind them. On clear film, unbacked ink lets light and the contents through, and colors can look thin. On metallized film, the metal shows through the ink and gives it a metallic cast.
Many laminated pouches are printed on the inside face of the outer film and then laminated to the inner layers. In that arrangement the colors are printed first and the white goes down behind them, so it is worth knowing whether your structure works this way.
This is why flexible-packaging printers ask for a map of where white prints, where metal shows and where the film stays clear. A published prepress checklist from one flexible-packaging printer, for example, requires clear areas to be identified and a white-ink separation to be included in the artwork. The separation shows where white ink will print and, just as importantly, where it will be absent. A separate file-setup guide recommends marking white-backed, unbacked and metallized areas distinctly.
White ink is a separation you approve, not a default
A white separation is the production instruction that tells the press where white ink prints. A white object in the design is not necessarily that instruction. Some printers want the designer to supply the separation under a specific spot-color name; others build it in prepress from the designer’s notes, so the file setup should be agreed before the artwork is finished. Using transparency settings to show a clear area is a common mistake; that same file-setup guide warns against it because the printer cannot reliably tell an intended clear area from white.
On an ordinary screen view, a white separation can be hard to see at all. If the PDF contains a separate white-ink plate, Adobe Acrobat Pro’s Output Preview can display it independently of the other separations, which shows where white ink is specified in that PDF. If the supplier creates or changes the white separation during prepress, request an updated separation proof before approving the final production file.
White backing changes how colors look, but it does not turn film into paper. White ink does not always completely hide the film or contents behind it. Its opacity depends on the ink and the printing process, so the expected appearance should be checked on a suitable physical proof or sample.
| Area | White backing | Expected effect |
|---|---|---|
| Printed graphics on clear film | Yes | Colors look more solid; the final look depends on the white’s opacity and the finished structure |
| Printed graphics on clear film | No | Graphics stay partly see-through |
| Printed graphics on metallized film | Yes | The white reduces the metallic effect behind the colors |
| Printed graphics on metallized film | No | The metal can show through the inks, often as an intended effect |
| Unprinted metallized area | No | The metallic surface stays visible |
| Clear window | No ink, no white | A see-through view is possible only if every layer in that area is transparent |
Registration at the edges. White and colored inks are printed separately and may not line up perfectly at their edges. This is a registration difference. Around small logos or fine text it can leave a thin white edge or an unintended clear gap, especially where the design moves between white-backed and unbacked areas.
Intended metallic areas. On metallized film, leaving white out under part of the design is a common way to make it shimmer. Mark these areas as intentional. Otherwise, whoever checks the proof may not be able to tell a planned effect from a missing white.
Codes. The same printer’s guidance asks for barcodes as vector art in 100% black. On clear or metallic film, a barcode also needs a solid contrasting background, and its readability is best confirmed by scanning it on printed material rather than judging it on screen.
Example: a clear pouch with a printed panel and a window
Consider a clear-film pouch with a colored front panel, black product text, a barcode and a transparent window.
The colored panel will usually need white behind it to look solid. The window has to stay free of both color and white. The barcode needs its own contrasting background instead of relying on whatever happens to sit behind the film. Before approval, request a separation view showing these areas. If a representative printed pouch sample is available, check it with the actual device inside.
If the design moves to a metallized structure, confirm how the clear window will be manufactured rather than assuming that leaving the area unprinted is enough.
Clear windows depend on the whole structure
A pouch is usually several layers laminated together, and the outer print film is only one of them. For a window to be see-through, the printer leaves that area free of color and white, and every other layer in that area has to be transparent too. A clear outer film on its own does not guarantee a window.
On a metallized structure, the metal layer is opaque, so the structure itself has to change. One option is to use a transparent structure and create the opaque areas with printed ink. This allows windows without removing any metal, but it does not give the same metallic appearance as a metallized film. Another option is a demetallized film, where the metallic coating is removed in selected areas to form clear zones. Demetallization is a material-processing step, not an instruction in the artwork. Whether it is available, and for which structures and window shapes, has to be confirmed by the supplier for your pouch.
Placement matters as well. The file-setup guide mentioned above advises never putting a window in a gusset. Seal areas can be printed but may distort slightly, so codes and critical text are safer elsewhere. Printing over a zipper is possible, but heat sealing can cause mild wrinkling there.
Finally, think about what will actually show through the window. Depending on where the device sits inside the pouch, the window may show the device, part of the opposite panel or empty space, and the view can change when the pouch is handled or stood upright. When available, a pouch sample packed with the actual device gives the clearest indication of what will be visible.
Brand colors on film need an agreed target and method
A brand color matched on coated paper will not automatically match on film, and it will look different again on metallized film without white behind it. Brand colors need both a defined reference and an agreed printing method.
The printer’s published file requirements mentioned earlier show how these two can differ. Pantone colors should stay identified as spot colors in the submitted artwork, but that does not necessarily mean they will be printed with separate spot inks: depending on the process, the supplier may reproduce them with process inks, including extended-gamut inks on some digital presses. The same printer requires a printed reference for custom spot colors; without one, its stated procedure is to convert them to CMYK. It is worth confirming early whether your supplier can reproduce the required color and which physical reference will be used for approval.
For critical brand colors, agree on a physical color target with the supplier. Where production-representative proofs are available, compare the printed result against that target under consistent lighting, not on a screen or in a photo. (ISO 3664:2025 is the current international standard for these viewing conditions; it does not cover on-screen soft proofing.) If the same brand color also appears on the hardware itself, that is a separate approval on a different material; see how to approve custom color and logo decoration on vape hardware.
What each proof or sample can and cannot show
A PDF can confirm text and layout but not how ink will look on film. A press proof shows more about the print, and a converted sample shows the pouch after assembly. Choose the proof based on what needs verification: artwork placement, printed color, metallic effects or the appearance of the assembled pouch. Suppliers use different names and methods, so the labels below describe what the proof includes rather than standard categories.
| Proof or sample | What you can assess | What remains open |
|---|---|---|
| Artwork PDF with separation information | Text, layout, dieline alignment, intended white and clear areas | Actual color on film, white opacity, finished look |
| Color proof on a proofing material | Approximate color intent under agreed viewing conditions | Exact reproduction on the production film |
| Press proof on the print film | Ink appearance and registration on the printed material | Effects of lamination and pouch conversion |
| Converted sample made with representative materials and processes | Finished appearance, window view, artwork placement and barcode readability on that sample | Production variation; seal strength, barrier, child-resistance or other performance not separately validated |
A proof’s usefulness depends on which production materials and manufacturing steps it represents; the name alone does not tell you what it demonstrates. A converted sample, for instance, may be made on the planned production route or may be a visual prototype made another way. As one published example, a printer describes its press proofs as printed on the unlaminated top layer of the chosen material and notes that adhesive and lamination can influence color. It supplies the laminate so it can be laid over the proof, which helps judge the expected look but does not reproduce the finished, converted pouch.
Physical proofs and samples can add cost and lead time, and not every supplier offers every option.
A practical approval sequence
- Freeze the structure. Get written confirmation of the film layers, clear or metallized, the finish and how any window is made.
- Set up the file to the printer’s instructions. Keep the dieline, printed artwork, white separation, clear areas and any finishing effects clearly distinguished, and ask prepress how each should appear in the production file.
- Check the separation view first. Before judging color, review the final separation information supplied by prepress, and confirm that white backing, transparent areas and intended metallic effects are correctly assigned.
- Choose the proof for the risk. For a critical brand color, an unfamiliar structure or a deliberate metallic effect, consider a physical proof or a production-representative sample, and agree on what it is meant to show before ordering it. For a repeat order, an earlier approved sample may be an appropriate reference if the supplier confirms that the artwork revision, material structure and relevant production method are unchanged.
- Check the product fit and window view when a representative sample is available. Pack the actual device into the pouch and inspect the window and artwork placement under the agreed lighting. Scan the barcode on printed material when available. If approval proceeds without a converted sample, record that the finished pouch appearance was not physically verified; if no printed barcode was tested, record that limitation separately.
- Record the boundaries of the approval.
Example approval record (illustrative only)
| Field | What to document |
|---|---|
| Final artwork | File identifier and revision approved |
| Material and production method | Supplier-confirmed structure and printing route |
| Evidence reviewed | PDF, color proof, press proof or converted sample |
| Checks completed | Specific items actually inspected and accepted |
| Checks not completed | Appearance or performance characteristics not verified |
| Authorization | Reviewer, approval date and supplier acknowledgment |
Before you sign
Three questions are worth answering explicitly at sign-off:
- Is the file being approved the final version after any supplier prepress adjustments?
- Does the reviewed proof represent the materials and processes specified for production?
- Which characteristics are outside the scope of this approval?
Then retain the final approved artwork, the approval record and any physical reference samples for production and future reorders.
For the material and construction details to prepare before requesting a custom pouch quote, see the custom Mylar bag options page.
References
- ePac Flexible Packaging, Prepress Checklist (dated 05.13.19): https://epacflexibles.com/wp-content/uploads/2020/02/Prepress-Checklist-Rev9.pdf
- ePac Flexible Packaging, 5 Common Pre-Press Mistakes to Avoid: https://epacflexibles.com/en-ca/5-common-pre-press-mistakes-to-avoid/
- ePac Flexible Packaging, Navigating the World of Press Proofs in Flexible Packaging: https://epacflexibles.com/navigating-the-world-of-press-proofs-in-flexible-packaging/
- ePac Flexible Packaging, The Significance of Press Proofs in Color Critical Printing: https://epacflexibles.com/the-significance-of-press-proofs-in-color-critical-printing/
- CarePac, Flexible Packaging Design File Setup: https://www.carepac.com/blog/flexible-packaging-design-file-setup/
- PFFC, “Opacity & White Ink”, January 1, 2008: https://www.pffc-online.com/print/5759-opacity-white-ink-0101
- PFFC, “Very Revealing” (selective demetallization for clear windows), October 1, 2009: https://pffc-online.com/first-glance/7559-very-revealing-1009
- Adobe, Previewing output (Adobe Acrobat Pro): https://helpx.adobe.com/acrobat/using/previewing-output-acrobat-pro.html
- ISO 3664:2025, Graphic technology and photography — Viewing conditions: https://www.iso.org/standard/83759.html
