A Guide for Understanding Common Paper Terms

Uncoated paper — sometimes referred to as offset paper — does not have any kind of coating or treatment on the surface to slow the rate of ink absorption. As a result, uncoated paper is more porous and allows for a greater amount of ink to permeate the fibers of the sheet. Because uncoated paper doesn’t use a coating, the texture of the sheet depends on how much the sheet is calendered, which is a process of passing the sheet through a series of rollers that use enough force to compress the fibers. A high degree of calendering makes an uncoated sheet extremely level and uniform, which can help create more consistent ink absorption and better image quality.

Opacity is a paper’s ability to obstruct light and minimize the potential for show-through. Paper opacity is measured as a percentage of light that cannot pass through the sheet. If a paper has a low opacity, it means the paper is more transparent. Opacity — or the lack thereof — is important in text-heavy print applications like book publishing or transactional print, as sheets that allow a lot of show-through can make the text difficult to read. 

Often confused with the thickness of a sheet, a paper’s basis weight is determined by dividing the weight of a ream (500 sheets) by the standard sheet size of that type of paper. Sheet sizes for different types of paper can vary greatly, and dividing the same weight by a different physical size will result in a very different basis weight. 

Aside from measuring the heft of your substrate, basis weight also impacts the overall print quality of your project. 

“In addition to selecting a paper weight for the general feel of the design or target mailing weight, the paper basis weight you choose for your job is crucial to the color, image, and finishing quality,” write Gooding and Schilling “The basis weight also has an impact on the opacity, with higher weight paper increasing the opacity of the sheet.” 

Porosity measures the ability of a sheet to accept water or ink, and it’s important because how much and how consistently the ink penetrates the paper affects color and overall print quality. Depending on how the paper was manufactured, porosity can also sometimes affect the color quality on one side of the sheet due to how quickly and thoroughly the ink dries. 

“Porosity is inkjet’s friend, but it’s a friend that must be closely managed,” write Gooding and Schilling. “Inkjet papers need some way to allow the ink carrier to absorb into the sheet when separated from the colorant. Without absorption, the beautifully formed and aimed dots would just roll off the sheet.” 

Gooding and Schilling refer to the smoothness of a sheet as the cousin of a sheet’s porosity — a smoother sheet provides a more consistent foundation for ink. For example, a smooth substrate is likely to have less porosity, which will then impact how much ink is absorbed in the fibers of the sheet. 

You can evaluate the smoothness of a sheet by touch and feel, but there’s also a numeric value assigned to how smooth or rough a sheet is. A higher number indicates a rougher texture, while a lower number means the sheet is smoother. For example, a very smooth coated paper might have a measure of 15, while a rough, uncoated sheet might have a measure of 250 or even higher. 

While opacity refers to light passing through a sheet, brightness represents the amount of light at the blue end of the color spectrum that is reflected from the paper’s surface. Traditionally, the measurement of a paper’s brightness is represented on a 0 to 100 scale, and the higher the number, the more brightness a sheet possesses. The brightness of a sheet is important because it affects how the human eye perceives ink color on the sheet.

For example, ink printed on a less bright sheet will produce colors that are dull and less vibrant compared to the same ink printed on paper with a higher brightness. 

Whereas brightness only measures the amount of reflected light from the blue end of the spectrum, whiteness accounts for all wavelengths of light. A paper’s whiteness more closely aligns with how the human eye perceives colors, and a measurement of a paper’s whiteness is a good indicator of the shade of any given sheet because it measures the reflectance of more than just the blue wavelength. 

The three varieties of whiteness — also referred to as shade — that are ideal for digital inkjet include true, cream white, and blue-white, and the differences between each of these can impact the perception of ink contrast. For example, using whiter papers can help improve contrast for darker images and accentuate more vibrant colors. 

Formulated specifically for inkjet, inkjet coated sheets come in a variety of surface finishes from very shiny (gloss) to less shiny (matte). The surface of inkjet coated stocks dries very quickly, which helps create a broader range of colors compared to uncoated sheets. The unique coating also helps make inkjet coated sheets more resistant to dirt, moisture, and wear.

Inkjet treated paper uses a treatment that blankets and seals the wood fibers. These treatments separate the colorants from their carrier liquids, which better allows the colorant to remain on the surface of the sheet and thus creates better print and image quality. Inkjet treated sheets also have a reduced porosity to prevent the ink from absorbing into the sheet along with the carrier liquid.