Print Your Plastic

Adding your company’s logo and other designs to your poly bags is a great way to customize and enhance your packaging products. This article will explain the various methods used in printing polyethylene film and bags.


Flexography, or flexo, is a common printing method in that it can produce large quantities of custom artwork at a fast rate. Polymer plates – consisting of a synthetic rubbery material – are engraved with your specific art. The plates are wrapped around a cylinder and installed onto the printing press. The cylinders rotate the plates through an ink tray, and as the film passes through the printing press and across each plate, an image and ink color is transferred  onto the film, ultimately resulting in a finished design of however many colors. Flexographic printing can print onto a variety of different materials and has a fast drying ink allowing for a fast production rate.

Here are some additional special terms that might help you navigate your way through flexographic printing:

Repeat Length – This is the distance from the beginning of one image to the beginning of the next. It is measured along the length of the roll of material.

Registered Printing – Registered flexo printing means the image will appear in the same location on every bag. This is done by synchronizing the plate and bag size to ensure that the image is pressed at regular intervals, ultimately producing the image in the same position every time.

Random Printing – Random printing means your logo or artwork will appear multiple times on each bag. The image will change position in a vertical or horizontal direction depending on if the bag is bottom-sealed or side welded. Some images may be partially cut off when the bags are cut and sealed since the images are randomly placed without regard to the sealing.

Slug Changes –  A slug refers to a very small printing plate, usually representing a small portion of an overall design.  A slug change refers to the the cost saving measure of changing out a portion of the artwork without having to create a whole new printing plate. For example, in the illustration below the client has advertised that Wednesday is Ladies’ Day and that the discount is 15%.  Let’s suppose that at some time in the future the client wishes to change the day of the week to Friday and the amount of discount to 25%.  Instead of incurring the cost of creating an entire new “Black” plate and “Red” plate (which would cost approximately $300), because flexo plates are rubber, or a synthetic derivative, it would be possible to simply cut out the “Wednesday” and the “15%” and replace them with the slugs,  “Friday” and “25%”.


Rotogravure printing differs from flexo printing in that the image is etched onto the plate in such a way that the image appears in the depressions instead of on the raised part of the plate. In flexography, the image is raised. With rotogravure printing, the raised, non-printing portions are wiped and scraped so ink only remains in the recesses of the plate and can transfer the image onto the material. Rotogravure is a beneficial and advantageous method of printing as it provides extremely high quality images and is good for long runs or runs that will repeat frequently.


Digital printing uses laser and inkjet printers to print images from a digital source. This form of printing typically has a higher cost per bag than other printing methods, but this cost is generally offset by foregoing the cost it takes to make printing plates. Not having to replace printing plates is the biggest difference between digital and more traditional forms of printing. Digital printing offers short turnaround times and even the option to modify the image used for each impression. Due to the rapidly increasing capabilities of the digital printing presses, digital printing is becoming an even more useful and common method of printing many images at a lower price.  

Printing CMYK vs. Spot Print Color

There are two different processes when it comes to printing color in your logo or artwork. Spot color printing consists of printing with one or more pre-mixed colors (a few colors all at once). This method uses a color system of solid, premixed colors known as Pantone colors. 18 basic colors are mixed to create a variety of precise solid colors in the Pantone Matching System. While spot colors are not able to be used in digital printers, they have many advantages. The colors are very accurate and will never change from one print run to the next. Spot color printing is also typically more economical if you are only working with three or less colors.

4-color process printing, or CMYK printing, uses the four colors: cyan, magenta, yellow, and black (also known as “key”.) These four base colors are used on their own, or are overlapped with one another to create a full color scheme. This process is typically used when printing photographic image types, or images with a lot of color depth and variety. Because of the overlapping of colored dots, image color may vary slightly from printer to printer, but 4-color process printing is most economical when working with lots of colors, and is the best for producing realistic photograph images.

Now that you are more educated when it comes to printing, consider Multi-Pak for your customized, printed poly bag. Multi-Pak has the capacity to print up to 8 colors and offers low minimum quantities on orders. As always, Multi-Pak has your order in the bag.

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