Detailed Printing Process Guide
What is Flexographic Printing?
Flexographic printing (flexo) uses raised-image photopolymer or rubber plates mounted on rotating cylinders. It's the most common method for printing on flexible packaging materials like poly bags, cellophane, and kraft paper.
When to Use Flexo Printing:
- Preprint Flexo: For 4-6 colors, tight registration, fine halftones (65+ line screen), lamination, or UV varnish
- Tailprint Flexo: For 1-4 colors during bag conversion, loose registration acceptable (3/32" tolerance)
- Medium-to-high volume runs (10,000+ units)
- Coated and uncoated papers, plastic films
Flexo Print Quality: Resolution of 65-133 line screen depending on substrate. Expect 9-15% dot gain on coated papers, 12-15% on uncoated. Registration tolerance: ±3/64" for preprint, ±3/32" for tailprint.
Flexo Advantages:
- Fast production speeds (up to 800 meters/minute)
- Works on virtually any substrate (plastic, foil, paper, film)
- Water-based and UV-curable inks available (food-safe options)
- Cost-effective for moderate-to-large runs
What is Gravure Printing?
Gravure printing uses engraved metal cylinders with recessed cells that hold ink. It's a preprint-only process ideal for high-volume packaging requiring premium color strength and fine detail.
When to Use Gravure Printing:
- Large production runs (100,000+ units) to justify cylinder engraving costs
- Up to 7 colors on one side (or 5 outside + 2 inside simultaneously)
- Metallic inks (gravure delivers superior metallic finish)
- High-resolution images (150-175 line screen)
- Coated papers only (claycoat substrates)
Gravure Print Quality: Minimal dot gain (3% dot prints as 5-7%). Very tight registration with minimal traps required. Excellent for dark colors and metallics where ink density matters.
Gravure Advantages:
- Highest color strength and density (best for metallics)
- Finest detail reproduction (175 line screen)
- Can print inside and outside of bags in one pass
- Registered inside print (not random)
- Long-lasting engraved cylinders for repeat orders
What is Offset Printing?
Sheet-fed offset lithography prints from flat metal plates onto individual sheets (not rolls). It's a preprint-only method offering the highest print quality for premium packaging.
When to Use Offset Printing:
- Small-to-medium runs (1,000-50,000 units)
- Unlimited color capability (sheets can run through press multiple times)
- Photographic quality required (150-175 line screen)
- Extremely tight registration (±0.010")
- High-grade smooth paper stocks
Offset Print Quality: Minimal dot gain (1% dot compensation possible). Precise ink metering via 9 ink rollers produces thin, uniform ink film. Best for fine gradients and photographic images.
Offset Limitations:
- Dark colors and metallics may require "double bump" (printing twice) for adequate density
- Higher per-unit cost for large runs vs. gravure or flexo
- Sheet-fed only (not compatible with continuous roll-to-bag conversion)
Choosing the Right Printing Method
| Factor |
Flexo |
Gravure |
Offset |
| Best For |
Moderate runs, bags & film |
High-volume, premium color |
Small runs, photographic quality |
| Quantity Range |
10,000-500,000 |
100,000+ |
1,000-50,000 |
| Color Limit |
4-6 colors |
7 colors (5+2 duplex) |
Unlimited |
| Resolution |
65-133 line screen |
150-175 line screen |
150-175 line screen |
| Substrates |
All (paper, plastic, film, foil) |
Claycoat paper only |
High-grade paper sheets |
| Registration |
±3/64" to ±3/32" |
Very tight (minimal) |
Extremely tight (±0.010") |
| Metallic Inks |
Good |
Excellent |
Requires double bump |
| Setup Cost |
Low-Medium |
High (cylinder engraving) |
Low-Medium |
Frequently Asked Questions
What is the difference between preprint and tailprint?Preprint means the roll stock (paper or film) is printed before it is converted into bags, which is required for 5 or more colors, tight registration, lamination, or fine halftones. Tailprint, available with flexo only, prints during bag conversion — faster and cheaper, but limited to 4 colors with looser registration (about 3/32" tolerance). Can you print on the inside of a bag?Yes, with gravure printing. Gravure can print up to 5 colors on the outside and 2 colors on the inside of the bag simultaneously, and the inside image can be registered (aligned) to the outside image rather than random. Flexographic and offset printing do not support inside printing. Which printing method is best for metallic gold or silver ink?Gravure delivers the strongest, most reflective metallic inks because its recessed engraved cells lay down more ink. Flexo metallics are adequate for most packaging applications. Offset metallics usually require a "double bump" — printing the color twice — to reach acceptable opacity and shine. What print resolution do I need for photos or gradients on packaging?For photographic quality use gravure or offset, both of which run 150-175 line screen. Flexo can reproduce photos at 110-133 line screen on coated paper, but expect visible dot gain of 9-15%. Supply vector artwork or images at 300 DPI or higher for the best result on any method. How much does custom printing on bags cost?Cost depends on quantity, number of colors, and method. Flexo and offset carry lower setup costs, roughly $200-$800, which makes them economical for smaller runs. Gravure requires cylinder engraving at roughly $2,000-$5,000 but delivers the lowest per-unit cost at high volume. Email [email protected] or call 570-709-0366 with your specs for accurate pricing. What artwork file formats do you accept for custom printed packaging?We accept Adobe Illustrator (.AI), print-ready PDF with embedded fonts, and EPS files. Build artwork in CMYK color mode with 1/8" bleed, and include Pantone (PMS) references for any spot colors. If you need design help, our prepress team can assist — email [email protected]. Related Packaging Resources
Ready to print your custom packaging? Call 570-709-0366 or email [email protected] with your artwork, quantity, and substrate. We'll recommend the best printing method and provide a fast quote.
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