Paper 101: What is basis weight, GSM, and other paper terms?

pressman_skids1-e1386707687808

A press operator looks at a printed sheet of paper.

Having been in print for 30 years, and with most of that in Production, I take it for granted that many laypersons have a very rudimentary knowledge of paper.  As digital has increased in its market share and is, in some cases, may be the only presses a printer may have, there have been changes in how paper is now specified.  So, in this blog post I’ll discuss the topics of Basis Weight, GSM, and coated vs. uncoated sheets.  Along the way you’ll gain knowledge and some terminology so you can effectively communicate with your print and marketing services provider.

ALEX, I’LL  TAKE PAPER VOCABULARY FOR $1000, PLEASE

  • Basis weight = and the question is, what is the weight of 500 sheets of paper at a specific size for a specific type of paper?
  • GSM  = and the question is, what is Grams per Square Meter, which is another way to measure paper density?
  • Parent Size = and the question is, what is the full-size or “parent size” of the sheet as it is sheeted at the paper mill?
  • Coated  = and the question is, what is the kind of sheet that has been run through a polishing process at the mill?
  • Uncoated = and the question is, what is the kind of sheet that has NOT been run through that special process?
  • Text or book  = and the question is, what is the kind of paper that is specified for the text or “book” pages of a booklet?
  • Cover = and the question is, what is the kind of paper that is thicker and used for book covers or other uses such as business cards or POP (Point of Purchase)?
  • Board grade = and the question is, what is the kind of paper that is thick and used for heavy-duty purposes, like packaging?

BASIS WEIGHT

What does it mean when you get a print quote back and it says “100# gloss cover” or “80# gloss text/book”?  Basis weight is calculated on a factor of 500 sheets, or a ream, of a specific paper at a specific “parent” size.  As you can see by the accompanying chart, parent sizes differ, but they are standard in the printing industry, and it is the “basis” of how the paper weight is calculated.  For example, in this chart, you can see that cover paper is calculated at 20 x 26″ parent size, so if you order 100# cover, 500 sheets at 20 x 26″ is 100#.  Oh, that “#” is not a hash-tag, but it is the way printers abbreviate pounds.  Now, if
you were to order that same 100# cover in a 26 x 40″ sheet size, but asked for the 100#, even though 500 sheets will twice as much, THE BASIS WEIGHT STAYS THE SAME, since it is calculated at a specific paper size.

 GSM, or g/m2

Digital printing still uses basis weight as a specification, but digital print presses, which have a wide use in Europe and other countries that are on the metric system, specify what papers can be used by the term GSM, or g/m2, or grams per square meter.  This figure is much more reliable, since it is not predicated on a specific parent-sized sheet, but on how many grams per square meter.  This is much more precise and accurate.  Digital presses (litho presses too for that matter) have minimum and maximum thicknesses that they can run through the press.  Digital presses for the most part have a minimum of about 75 GSM, and a maximum of about 350 GSM.  It would be advisable to check with your marketing services provider to ascertain what is their device’s minimum and maximum GSM.

COATED VS. UNCOATED

For decades there were just a few terms that you needed to know about paper coating: book, text, cover, coated or uncoated.  But as digital continues to increase in use and market share, the terminology has altered slightly, and includes the term “text”, which clients mean “non-cover” stock.  But the issue is that in specifying simply “text”, it is not clear whether it’s coated or uncoated.  Therefore, it’s crucial to specify “gloss text” or “uncoated text” in quote requests.  Cover still remains the same, with clients specifying coated or uncoated.  Plus, there are different types of coatings that can be specified, such as gloss, dull, silk, or matte, and they can be very subtle in their differences.  Some mills will have their silk be close to a matte, or another might have their dull be close to a silk.  Also, the type of coating can have subtle differences in how ink lays down on the paper.  It’s beneficial to have your provider give you a swatch book sample of various types of papers so you can have a reference, touch and feel the coatings, and be able to specify which kind of coated paper you desire.  The process of coating a sheet is actually not an accurate description.  Coated sheets are run through a milling process which basically “polishes” the sheet, and the amount of polishing, or the texture of the polishing rollers, can determine how the coating looks on the sheet.

THE DAILY DOUBLE

Packaging products are printed on what is called “board grade” stock, which gives an impression that the paper is less than high quality.  On the contrary, some board grades have excellent coated surfaces which handle ink well, and are the primary types of sheets used for packaging due to their thickness and durability.  Most board grades are sold as either C1S, or coated one side, or C2S, which means coated two sides.  They are specified by thickness, not basis weight or GSM, and start usually at 10 point, or .010″, then there’s 12 point, 14 point, 15 point (usually only C1S), then 16 point, 18 point, and then 24 point.  Most litho presses cannot print more than 24 point, although some can handle up to 48 point board.  Those presses are specifically packaging presses.

FINAL JEOPARDY

The best thing a print buyer or designer can do is secure paper swatch books, either from their printer or the paper companies such as Neenah, Fox River, and others.  However, keeping those books up-to-date is crucial, since mills – particularly overseas mills – will change paper frequently and what you see in a book from 2011 may be discontinued.  Again, just contact your printer for up-to-date swatch books.

Connect with John on Google+Twitter and LinkedIn.

Advertisements

About John Prothero

John Prothero is a print professional with over 30 years experience in the print industry. Starting out as a driver delivering jobs, he worked in bindery, proofing, plating, traditional prepress (camera and stripping), scheduling, job planning, job management, account management and digital job production. His skills also run in the area of blog authorship, social media management, and lead generation and qualification of prospective clients. John is also a contributor to Rhode Island Creative Magazine, a digital publication that highlights the creative spirit of the state of Rhode Island. You can read their online issues at www.ricreativemag.com
This entry was posted in Paper, Print and tagged , , , , , , , , , . Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s