White ink and underprint on clear and metallic packaging
Send a design you love to a converter for a clear film pouch or a foil label, and it can come back looking like a faded ghost of the file you approved on screen. The usual culprit is a missing white layer — here is what underprint white does, when you need it, and how to build it so your color reads true.
THE SHORT ANSWER
On clear film, foil, metallic, or kraft substrates, printed colors go transparent because there is no white background to reflect light — so an opaque white ink layer has to be printed first, underneath the color. You have to spell that white layer out in your file as a named spot color on its own layer, or the press has nothing to build it from.
- Underprint white is the opaque base that makes color read true on any non-white substrate
- Flood white covers everything; spot white is shaped for a deliberate no-label or clear-window look
- Build it as a spot (commonly named "white"), on its own layer or separation, set to overprint — never mixed from CMYK
- Registration matters: choke or spread the white so normal misregistration never leaves a white halo
What underprint white actually does
Most printing ink is translucent. On a sheet of white paperboard that hardly matters: the bright white substrate reflects light back up through the ink, so a cyan looks like cyan and a red looks like red. The paper is doing half the work. Take that white background away — print onto clear film, brushed foil, or brown kraft — and the same ink has nothing bright behind it to bounce off. The color turns weak, dark, and see-through, and whatever is behind the package shows straight through the artwork.
White ink is the fix. Unlike process colors, it uses a highly opaque pigment, and it is laid down first — under the color — to create a bright base where the substrate can't provide one. That is where "underprint" comes from. On reverse-printed film (art printed on the inside of a clear web so the film protects it) the white images last on press but ends up sitting behind the color in the finished pack. Either way the job is the same: give the color something white to sit on so it reads the way it did on your monitor.
Getting white right is one of the print-quality fundamentals we cover in our complete guide to packaging print & quality. It sits right next to color management and registration, because a white layer that is patchy, thin, or misaligned undermines every color printed on top of it.
When you need white ink
The rule of thumb is simple: if the substrate isn't already bright white, plan for white ink under any color you want to read solidly. The most common cases:
- Clear film — transparent PET, BOPP, or PE used for windows, shrink sleeves, and see-through pouches. Without white, the color looks tinted and the shelf behind it shows through.
- Metallic and foil substrates — metallized films and foil boards. Color printed straight onto metal takes on a metallic sheen (sometimes the goal, often not); white knocks the shine back so a color reads as a true, flat color.
- Kraft and other colored stocks — brown kraft, colored paper, or a dark board darken and mute anything printed on them. White gives light colors a fighting chance and lets you print anything other than dark tones.
- Direct-to-container clear glass or plastic — decorating a clear bottle or jar has the same problem as clear film; a white base is what makes a printed color opaque on glass.
When you don't need it is just as useful to know. A white paperboard carton, white BOPP label stock, or coated white paper already gives you the reflective base, so a full flood of white is wasted ink and an extra press station. The flexible-packaging structures where this matters most are worth understanding on their own — see our overview of flexible packaging types for how clear, metallized, and white-film webs differ.
Flood white vs spot white
There are two ways to lay the white down, and choosing between them is a design decision, not just a production one.
Flood white covers the entire printable area with a solid white layer, as if you were manufacturing your own white substrate on top of the clear film. It is the simplest thing to build and the safest default when the whole face of the pack is printed. The downside is that you lose the transparency of the film entirely — the pack no longer looks like clear film at all.
Spot white (sometimes called shaped or selective white) prints white only where you actually need it, leaving the rest of the substrate bare on purpose. That is how you get the sought-after "no-label look" on a clear pouch or bottle: the product shows through the unprinted window while the graphics, logo, and legal copy sit on their own little islands of white so they stay legible. Spot white is more work to plan, because every colored element needs a matching white shape behind it, but it is the only way to keep a genuine clear window.
A related question is how much white. A single pass on a very transparent or metallic substrate is often not opaque enough, so printers frequently lay down a double hit — two passes of white — to build density before the color prints. One hit or two depends on the press, the ink, and the substrate, so treat it as a conversation with your converter, not a fixed rule. It has a cost consequence too: more coverage and more passes mean more ink and sometimes an extra press station, which is why heavy flood white on a many-color job is worth pricing on the real run with an instant quote.
How to build white ink in your file
White ink is not a color you can leave to chance in the file. The press images it from its own separation, so it has to exist as a distinct, named object — not as an absence of ink and not as a mix of CMYK. Here is the production-standard way to set it up:
- Make a named spot color. Create a spot swatch, commonly called simply "white" (some converters ask for a specific name like "Spot White" or "PMS White" — confirm theirs). This is the plate the white prints from.
- Put the white on its own layer. Keep every white shape on a dedicated layer or separation, above or below the color art per your converter's convention, so prepress can isolate it cleanly. This mirrors the way a cut path lives on its own layer on a dieline.
- Set the white to overprint. White is usually set to overprint so it doesn't knock a hole in whatever is beneath it and the color can sit directly on top. Never build white from CMYK values — that produces a "false" white that images on the color plates instead of the white plate.
- Choke or spread for registration. Because no press registers perfectly, the white is usually choked a touch smaller than the color it backs (or the color is spread slightly over it) so a small amount of drift doesn't reveal a bright halo at the edges.
- Confirm one hit or two. If the job needs a double hit, prepress may build a second white separation. Flag your opacity intent so they can plan the passes.
The mechanics of spot separations — how a named spot differs from a process build and why it images on its own plate — are the same ideas behind spot color vs CMYK. And the file hygiene that keeps the white separation intact through export is exactly what a print-ready PDF for packaging is meant to preserve.
White ink by substrate: clear film, foil, kraft
The reason you need white and the way it is usually built change with the material. This is the short version; the material families themselves are covered in our label materials guide.
| Substrate | Why white is needed | Typical white approach |
|---|---|---|
| Clear film (PET, BOPP, PE) | No white base; the shelf and product show through and color goes translucent | Flood white behind all art, or spot white shaped for a clear-window "no-label" look; often a double hit for opacity |
| Metallic / foil | Color takes on the metal's sheen and reads inconsistently | White under the areas that must read as a flat, true color; leave white off where you want the metallic effect to show |
| Kraft / colored stock | The dark or brown substrate mutes and darkens every color on top | White under light or bright colors so they don't disappear; dark inks can often print straight onto kraft with no white |
| Clear glass / plastic containers | Same as clear film — the color has nothing opaque behind it | A white base printed first (screen, pad, or digital) then color over it |
| White paperboard / white BOPP | None — the substrate already reflects light | No flood white needed; save the ink and the station |
Common white-ink mistakes
Almost every white-ink problem traces back to a handful of file errors. Here are the ones converters see most and how to head them off.
| Mistake | Why it fails | Fix |
|---|---|---|
| White built from CMYK | It images on the color plates, not the white plate, so no real white prints | Use a named spot color for white; never a process mix |
| White set to knock out | The white cuts a hole in the layers beneath instead of backing the color | Set the white spot to overprint per your converter's setup |
| No choke or spread | Slight misregistration reveals a bright white halo around the color | Choke the white slightly, or spread the color, to absorb drift |
| Single hit expected to be opaque | One pass on clear or metallic looks thin and washed out | Plan a double hit where opacity demands it; ask the converter |
| White missing under a barcode or light copy | The code won't scan and light text vanishes on the bare substrate | Back barcodes and critical copy with white so they read against the substrate |
| Flood white on a white substrate | Wasteful ink and an extra station for no visible benefit | Drop the white layer when the stock is already white |
How PackOS handles white and underprint
Because PackOS is built to read a real production file, it treats white as a first-class separation rather than an afterthought. When you upload artwork, it classifies the layers and spot separations — including a white plate — and can flag when a color-heavy design is heading for a clear, metallic, or kraft substrate with no white behind it, which is exactly the situation that prints see-through. The 3D proof renders the white in place, so you see the pack the way it will actually look on that substrate, not on an imaginary white background. You can see how that detection works on the technology page, or run it on a real file with Quick Quote and get a price at the same time.
Frequently asked questions
Why do printed colors look see-through on clear film?
Clear film has no white background to reflect light back through the ink, so process and spot colors sit as translucent layers and whatever is behind the package shows through. Without a white ink printed behind them the colors look weak and washed out. A white underprint gives the color an opaque base to sit on so it reads true.
What is the difference between flood white and spot white?
Flood white covers the entire printable area with a solid white layer, as if you were faking a white substrate. Spot white is shaped to only the areas that need it, leaving the rest of the film clear on purpose. Flood white is the simplest to build, while spot white lets you keep a deliberate no-label look where the substrate stays transparent.
Do I need a double hit of white ink?
Often yes. A single pass of white on a clear or metallic substrate is usually not opaque enough on its own, so printers frequently lay down two hits of white to build density. Whether one or two passes are needed depends on the press, the ink, and the substrate, so confirm the build with your converter.
How do I set up white ink in my artwork file?
Create a named spot color, commonly called white, and place the white shapes on their own layer or separation set to overprint. Do not build the white out of CMYK. The prepress team uses that separation to image the white plate, so it has to stay distinct from the color art rather than be mixed into it.
Does the white layer have to be exactly the same size as the color art?
Not exactly. Because no press registers perfectly, the white is usually choked slightly smaller than the color it backs, or the color is spread over it, so a small amount of misregistration does not leave a white halo at the edges. Your converter can apply the choke or spread if you flag the white as its own spot separation.