“Some lines are too thin to print.”
Lines thinner than about 0.25 pt (0.09 mm) can print broken, faint or not at all, so printers flag them as hairlines. White lines on a dark background, lines made from more than one ink, and lines on uncoated paper or labels need more, often 0.5 pt or heavier. The fix is to find every thin stroke and thicken it to your printer’s minimum, which usually takes minutes in Illustrator or Acrobat Pro.
Updated November 3, 2026 · by Azaan Ali, print designerWhy printers ask for this
On screen a line has no minimum size: zoom in and even a 0.1 pt line looks solid. On press it has to be made of real ink on a printing plate, and below about a quarter of a point there isn’t enough of it to hold. Thin lines break up, print unevenly or disappear, especially when ink spreads into uncoated paper.
Hairlines usually arrive by accident: a logo with a 1 pt outline scaled down to 20% (it becomes 0.2 pt), a border set to “hairline” or 0 pt, or a thin keyline from a template. A 0 pt or hairline stroke prints at the thinnest line the output device can make, which on a high-resolution platesetter is close to invisible. White lines reversed out of a colour fill in even sooner, because the ink around them spreads inwards.
How to fix lines that are too thin to print
- Check your printer’s minimum. 0.25 pt (0.09 mm) is common for dark lines on light paper; reversed lines, lines in more than one ink and flexo labels often need 0.5 pt or more. Screen printing, foil and embossing need much heavier lines, so ask.
- Illustrator: select one thin line, then Select → Same → Stroke Weight to select them all, and set a heavier weight in the Stroke panel.
- Before scaling artwork down in Illustrator, check Preferences → General → Scale Strokes & Effects. When it’s on, strokes shrink with the artwork and a fine line can drop below the minimum.
- Thin filled shapes (fine type, outlined strokes) can’t be fixed with the stroke weight. Add a stroke in the same colour to thicken them slightly.
- InDesign: check table strokes, paragraph rules and frame strokes in the Stroke panel, and raise anything under the minimum.
- Acrobat Pro: Print Production → Fix Hairlines replaces every line under the width you choose with a heavier one, right in the PDF.
- Keep fine lines and small text in one ink (100% K or a single solid colour), never a four-colour mix, so they can’t print out of register.
Or send it to us
- Find every stroke and sliver under your printer’s minimum, including inside placed logos
- Thicken them without changing the look, adjusting the design where a heavier line would crowd it
- Set fine lines and small text in a single ink so they print crisp
- Check white (reversed) lines and text against the heavier minimum
Questions
- What is the minimum line thickness for print?
- Around 0.25 pt (0.09 mm, or 0.0035 in) for dark lines on light paper in offset and digital printing. Many printers ask for 0.5 pt for reversed lines, coloured lines and labels, and screen printers and foil makers want more. Your printer’s spec sheet has the exact number.
- What does “hairline” mean in a print file?
- Either any line below the printer’s minimum, or a stroke literally set to “hairline” or 0 pt, which tells the output device to draw the thinnest line it can. Both get flagged, because neither prints reliably.
- My lines look fine in the PDF. Why is the printer worried?
- Screens draw every line at least one pixel wide, however thin it really is. The printer’s preflight measures the real width. Acrobat’s Enhance thin lines setting (Preferences → Page Display) makes thin lines look heavier still, so turn it off to see them more honestly.
Terms on this page: Hairline, Registration, Vector.
Other things printers say
More on this kind of work: Print file fixing.
Not sure what your file needs?
Ask a question or send the file in the chat. A designer answers right away with a fixed price, and nothing starts until you say yes.