Gustavo BanerTeam ColorCopiesUSA.com
Date Published: 2020-03-01 // Updated: 2020-07-29
The way in which we identify paper here in the USA frustrates many people. Most of the world utilizes the metric system which is based on a simple concept that makes easier to identify and compare papers.
In the US, we use a nomenclature related to the manufacturing process.
After reading this article you'll be able to differentiate paper by types, thickness, weight, application, finishing, and use. You will be able to compare how paper in the USA is identified elsewhere. You will be able to answer questions such as "How is a 20# (pound) copy bond paper different from a 60# offset paper?"
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All About Paper Weights: Understand "Basis Weight", Bond, Book Grades, Text Grades, Cover Stock, Index and Tag.
We will start by analyzing the weight of the paper, which creates the most headaches to our clients. We'll talk about paper production, finishing and brightness as well so that you have a broad knowledge about paper in the printing industry
U.S. Basis Weight is defined as the weight of 500 sheets of paper in its basic production size (parent size), before any cuts take place. Find the Chart of Paper Manufacturing Sizes on this same page.
- Example #1: Basis Weight of Bond Paper: A sheet of bond paper comes out of a production line and measures 17x22 inches. If the weight of 500 of those sheets is 20lbs, that bond paper will be identified and labeled as “20lbs”, or “20# bond”.
When you cut the 17”x22” sheet into two, you will get 2 sheets each measuring 8.5”x11” which happens to be a “letter size”.
Assuming that we have those 500 uncut sheets, we’ll end up with 1,000 sheets of 20# bond paper. Each group of 500 sheets then weighs 10 lbs.
Conclusion: The Basis Weight of Bond paper is 20lbs.
Same paper, different origin though: This is curious and confusing: If the same components to the paper and the thickness kept, were produced out of a sheet of paper that measures 25 x 38 inches, 500 sheets of that paper would weigh 50 lbs. It would be 50lbs basis. So as you can see, the paper, physically, would be the same. But its name would be 50 lbs. instead of 20 lbs.
The physical weight of those sheets would still be 10lbs.
The number itself is not indicative of how thick one paper is when compared to another one.
- Example #2 for 100 lbs coated paper: We will find out the basis weight of a coated sheet of paper. Here is an illustration that helps visualize this. Coated paper is manufactured in sheets of 25 x 38 inches. In this case, 500 of those sheets weigh 100 lbs. Therefore the Basis Weight for this paper is 100 lbs, also known as 100# coated text paper.
Chart of Paper Manufacturing Sizes
Useful to determine Basis Weight and Parent Sizes
Paper is Manufactured at Paper Mills Using Different Machines With Different Technologies.
There are several stages in the manufacturing process with 'finishing' being the last one. Wood chips get transformed into pulp, rollers calender the paper and determine the thickness of the paper. During the production and finishing processes, the softness is determined. For glossy or satin paper, a coating gets added to complete the process. Therefore different machines in different widths produce different types of paper. The end product at the mill is a roll that gets trimmed into flat sheets comprising what is known as the parent size.
Names and Sizes of Paper in the US Standard System
The way to obtain different sizes of paper is by cutting the parent size into fractions. The typical way is to cut the mother sheet in half.
U.S. Standard Paper Sizes
|Ledger||279 x 432||11 x 17|
|Legal||8.5 x 14|
|Letter||216 x 279||9.5 x 11|
|Monarch||7.25 x 10.5|
|Executive||140 x 216||5.5 x 8.5|
|Statement||108 x 140||4.25 x 5.5|
|Business Card||2 x 3.5|
The U.S. Standard System changes the proportions of the sheet of paper once it is cut in half making it difficult to size up or down
The International Systems for paper weight and sizes is designed so that cutting paper in half still keeps the same proportions. That system is known as ISO "A"
The Grades of Paper are defined in terms of its use. Each grade serves a purpose:
- Opaques and Offset Papers
- Coated Papers
- Writing Papers (a.k.a. Correspondence Papers or Bond Papers)
- Text and Cover papers
Opaques and Offset uncoated papers: These are similar with some specific differences
Offset uncoated papers are commodity papers available in large volumes. Over the years a change in formulations made it alkaline as opposed to acidic, which gives it better archival properties. Their internal bonding is good, with high surface strength and dimensional stability.
Offset Paper: Typical basis weight for this paper are 50lbs, 60lbs, 70lbs, 80lbs
The finishes of offset papers are
- Vellum finish which is extremely rough
- Patterns: as in Laid and Linen finishes
Opaque Paper:Typical basis weight for this paper are 50 lbs, 60lbs, 70lbs, 80lbs
- Film Coat
- Thin Coat
Coated Papers have 5 types of finishing and 5 qualities
Coated papers are made like offset papers but have a clay coating added on their surface before calendering. The coating creates a gloss or sheen on the paper's surface. This coating holds ink better and helps get a smaller dot that in turn produces a better printing quality. The clay often accounts for as much as half of the weight of the paper. Therefore the quality of the clay determines how bright, printable and strong the paper will be (resistance to tear, shear, etc)
The calendering process produces the following types of finishes
- Cast Coated, which are very shiny
The quality is determined by the brightness, smoothness, mechanical properties (resistance, shear, etc) and stability of thickness among others. Paper is rated from 1 to 5, 1 is the highest quality. 5 is the lowest quality
Optical Properties: Brightness
Paper brightness is a very important property in the paper. For certain applications, users usually assign a higher quality to paper that looks whiter with a shade of blue.
Brightness measures how much of the blue light in the spectrum reflects on the paper.
The scale goes from 0 to100. Brightness 100 is a very white bluish-tone paper.
Uncoated paper: Some premium uncoated papers (made just out of pulp) have very high brightness.
Coated paper: The coating used is clay. Their brightness values are in the low-mid 90's for a good quality paper.
Thick cardstock: It is usually a lower-brightness product.
Writing Paper also known as Correspondence Papers or Bond Papers
This writing grade historically called Bond papers are designed for letterhead, corporate identity, and home or office printers. They perform well for handwriting. These can be done with a watermark or can have cotton fiber to provide an elegant feel and mechanical strength.
Text and Cover papers
These are premium uncoated papers that are available in amazing colors and finishes. Some text papers are lighter, while Cover papers are thick and nice for covers, brochures, and business cards.
Basis weights that are equivalent
Because paper mills produce with different technologies, similar end-use paper could have come from parent-sheets with different sizes. Here is a list of equivalent grades, produced in different mills. The column on the right side, identified as METRIC is the favorite in countries that have adopted the International system. That system provides the weigh of a certain size expressed in grams, regardless of the method of production.
|US Basis Weights||Caliper||Metric|
|Bond||Text||Cover||Index||1 Point = 0.001"||GSM (g/m2)|
There is so much more to paper that can be said and reviewed.
Please visit the Printing 101 Academy to find more technical articles.