What is the ΔE*ab value and how does it affect print quality?

ΔE*ab is a standardised metric used to measure the difference between the intended colour and the colour actually printed in the CIELAB colour space. Values up to 5 are within the printing standard, whilst a deviation above 5 is already noticeable to the human eye. We include this parameter directly in our quotations for bespoke paper bags.

Why do white paper bags come in different shades of white?

The different shades of white are caused by optical brightening agents (OBAs), which are added to the paper pulp and enhance the white colour through fluorescence. The amount of these substances varies depending on the type of paper; for this reason, an ExtraTWIST bag, for example, may have a different shade of white to a Twister bag.

What is metamerism, and why do colours look different in the sunlight?

Metamerism is a phenomenon whereby two pigments with different chemical compositions appear identical under artificial light, but their differences become apparent in daylight. This is most noticeable in papers with a high content of optical brightening agents (OBAs), as they react to the UV component of sunlight.

What is the difference between printing on paper and cotton bags using the same colour?

Cotton absorbs more ink and creates a matt, textured finish due to a phenomenon known as the ‘hook-and-loop’ effect, whilst paper is less absorbent and the ink forms a smoother, glossier film on it. Therefore, to achieve the same visual effect on both materials, we mix the inks differently.

Which printing technology should you choose to ensure true-to-life colours on brown kraft paper?

For brown kraft paper, we recommend screen printing using PANTONE C inks, which offer high opacity and are not affected by the colour of the substrate. In contrast, flexographic and digital printing are less opaque processes, where the brown substrate will always have some influence on the final colour.

Why might bags from the same product range vary slightly in colour?

Despite the strictest colour control, minor variations can occur during paper production and printing due to the effects of light, humidity or temperature during storage. Consequently, for example, a blue ExtraTWIST bag produced in January may be a slightly different shade to the same bag produced in September.

Not all whites are the same: Metamerism and the ΔE*ab deviation in practice

We care about your promotional bags looking exactly as you envisioned them. In previous articles, we discussed color swatches and print data, but today we'll look at why, even with the best effort, 100% color match cannot be guaranteed across all materials and production batches. Do you know what the ΔE*ab color deviation is and why the color changes depending on whether you're standing in an office or outside in the sun?

What does the ΔE*ab value tell us?

In printing, we use the ΔE*ab metric (in the CIELAB color space) to measure the difference between two colors. It's a standardized calculation that helps us compare the intended graphic design with what was actually printed on the paper bags.

How to interpret these values in printing?

ΔE*ab 0–1: Imperceptible deviation.
ΔE*ab 1–2: Very small deviation (only distinguishable to a trained eye).
ΔE*ab 3–5: Medium deviation – the difference is visible, but still within print standards.
ΔE*ab > 5: Unacceptable deviation that is unpleasant to the human eye.

For the production of custom-made machine-made paper bags, we often state this parameter directly in the price quote so you can be sure of the quality of the output.

The color deviation ΔE*ab is measured as the spatial distance between two points in the CIELAB space. The space is three-dimensional and consists of three axes:

L* (Lightness): Expresses brightness, ranging from 0 (absolute black) to 100 (brightest white).
a* (Green-red axis): A value of 0 is neutral gray. Negative values represent green, and positive values represent red.
b* (Blue-yellow axis): A value of 0 is neutral gray. Negative values represent blue, and positive values represent yellow.

CIE Lab colour space — *Graphic representation of the CIE Lab model*

What about the coloring of our bags in the e-shop?

We try to keep the color as consistent as possible across all our production batches. Still, during paper production and subsequent printing, minor deviations occur. What does this mean in practice?

For example, the blue paper bag ExtraTWIST produced in January may have a slightly different shade than the same bag produced in September. External influences such as light, humidity, or temperature are also to blame, which we take into account in our warehouses to prevent color degradation. Still, if you place a small and large blue ExtraTWIST bag from different batches side by side, a sensitive eye might notice a slight difference.

The same applies to white. White paper bags may have different whiteness levels depending on how the paper was manufactured and stored. So it may happen that the ExtraTWIST paper bag has a different shade of white than the white Twister bag. Our goal is to minimize these differences, but we cannot guarantee 100% identical matching across the entire product range.

Why is some paper "whiter" than white?

You may have noticed that some white bags appear brilliantly clean, while others look yellowish or grayish next to them. This effect is caused by optical brightening agents (OBA – Optical Brightening Agents). These are substances that work on the principle of fluorescence: they absorb UV radiation invisible to the human eye and convert it into visible blue light.

Our brain perceives this blue reflection as bright, brilliant white. You can find them everywhere around us – in laundry detergents to make shirts shine, and in office and coated papers to make them look premium. In printing, these brighteners are added directly to the paper pulp in the form of fibers that compensate for the natural yellowish tint of cellulose.

Watch out for light: It is precisely in papers with a high OBA content that metamerism is most pronounced. Because these substances react to the UV component of light, a bag will look different under daylight sun (which has a lot of UV radiation) than indoors under a regular LED bulb, where it will appear "warmer" and less brilliant.

White tiles — *White bags that have a different content of optical brightening agents.*

The trap called metamerism: Why do colors "lie" in the sun?

Has it ever happened to you that a black jacket and black trousers matched in the store, but in daylight each piece had a different tint? That's metamerism. This phenomenon occurs when two pigments have different chemical compositions. Under artificial lighting, they fool the brain, but cool sunlight immediately reveals their difference. That's why our designer canvas bags or gift bags are evaluated under standardized lighting.

Absorbency and texture: The difference between paper and cotton

Do you want to print the same corporate logo in PANTONE C on paper bags and cotton bags? We know how to handle that. For each material, we mix colors differently to achieve the same visual impression for the human eye. Learn more about PANTONE colors in our article about color swatches.

However, absorbency plays an important role:

Printed canvas bags: Cotton fibers absorb a larger amount of color. This creates a "Velcro" effect – the cotton captures the color and doesn't release it back to the surface. The surface isn't smooth, which causes different light refraction than on paper.

Printed paper bags: Kraft paper is less structured, so the color forms a smoother film on it and doesn't look as "matte" as on textile.

Choosing the technology: What color will you get?

When choosing a paper bag, the selected technology and its opacity play a crucial role:

1. Flexography: Ideal cheap eco print

This technology is great for large runs (over 1,000 pcs). It uses water-based inks (PANTONE U color chart). These inks soak into the structure of the paper and do not create a strong film on the surface of the bag, so the resulting color is affected by the color of the printed material.

Result: If we print white color on brown promotional bags, the result will be a "natural" white, not a bright snowy white. It is ideal for companies who want their eco bag to look natural.

2. Digital printing: Watch out for the brown base

We digitally print CMYK inks. You can find out more about this color space in the article The secret of perfect printing: Why does the monitor glow?.

Result: The inks are not very opaque. If you want to preserve color fidelity and vividness with digital printing, we recommend choosing white paper bags. Printing on a brown base will always be affected by the brown color of the paper.

3. Screen printing: Premium quality and high opacity

If you are looking for luxury paper bags or want cotton bags with custom print with an absolutely precise logo, choose screen printing.

Result: We use PANTONE C spot colors, which have high viscosity and opacity. The color stays on the surface as a smooth, glossy film. With screen printing we can print both shoulder fabric bags and machine paper bags and luxury gift bags, while the color of the base does not affect the result.

Need help with your choice?

Are you lost and not sure whether an unprinted linen bag or a printed one is better for you? Our team of experts will recommend the ideal printing technology based on your design.

Whether you are looking for gift bags, Christmas bags, or a linen bag with print as a gift for your employees, just send us an inquiry with your design to [email protected]. On our e-shop, you can also use the "inquire with print" button on a specific product. We will promptly send you a non-binding tailored price quote!