You might have noticed that when you tear a square from a sheet of paper, one direc­tion leaves a nice clean edge but the edge is much more ragged on the right-angled tear.  You’ll have also spot­ted that when fold­ing A4 sheets in to A5 book­lets there’s a strong ten­den­cy that the book­let will spring open.  Paper dis­plays dif­fer­ent qual­i­ties depend­ing on whether you’re work­ing in the direc­tion of the ​‘grain’ or ​‘across the grain’.

Because paper is made from long fibres of one form or anoth­er, there is a ten­den­cy for paper machines to draw these fibres in to the machine in a par­tic­u­lar direc­tion.  Nat­u­ral­ly paper­mak­ers look to avoid this but even in fine papers you’ll end up with long fibres run­ning in the same direc­tion as the paper machine runs.  This is the ​‘grain direc­tion’.  There’s no firm rule about which direc­tion the grain will run in any giv­en pack­age, but paper mer­chants tend to cut the paper so that the grain runs from top to bot­tom.  On larg­er sheets that you might buy direct­ly the grain could run in either direc­tion.

There are two sim­ple tests to find grain direc­tion.  If you tear the paper once and again at right-angles, you’ll see that the tear looks dif­fer­ent: with the grain will leave a much clean­er tear; across the grain will leave a more messy tear.  Alter­na­tive­ly you can cut two sim­i­lar pieces of paper around 2″ x 6″ at right angles to each oth­er and put them togeth­er.  Hold­ing one end out you’ll find that one might flop and anoth­er seem more strong; if not one might be ​‘sup­port­ing’ the oth­er.  This ​‘sup­port­ing’ or stronger piece will have the grain run­ning down the length of the paper.

Grain direc­tion will affect ten­sile strength; rigid­i­ty and sta­bil­i­ty.  The degree to which these affect us will depend on the spe­cif­ic paper and mak­er so there are no con­crete rules on how big a prob­lem this might be for you.

Strength will be most impor­tant in some spe­cial­ist appli­ca­tions: bot­tle labels, for exam­ple, are applied left-to-right on the bot­tle and so are pulled from left-to-right by the labelling machine.  Because the paper will be strongest with the grain, it should be print­ed so that the grain runs from left-to-right.  Oth­er areas might include hole punched doc­u­ments that might be sub­ject to pulling from left-to-right.

To pre­vent ​‘spring­ing’ when a book­let is opened; the grain should run par­al­lel with the spine.  Look out for this if you intend to print, say, an A5 book­let from A4 because the A4 is usu­al­ly sold with the grain run­ning from top-to-bot­tom.  Using this will lead to the fold­ed book­let spring­ing open.

Rigid­i­ty is impor­tant where print­ed arti­cles have to be han­dled or stored upright.  Index cards, for exam­ple, need to be print­ed with the grain run­ning from top-to-bot­tom as this will mean the card is strongest in this direc­tion, and so avoid the cards flop­ping down or curl­ing slight­ly.  Clock­ing-in cards should be print­ed with the grain run­ning top to bot­tom to help with the han­dling of the cards.

Final­ly, sta­bil­i­ty rests on the ten­den­cy of paper to take up water from its sur­round­ings.  When this hap­pens the paper swells across the grain because fibres have a ten­den­cy to expand in their width rather than length.  This is most impor­tant when doing very close reg­is­ter work or colour print­ing.  There may be a direc­tion where the reg­is­ter is less impor­tant.  One exam­ple would be ledger sheets where top-to-bot­tom reg­is­ter is less impor­tant than the need to get left-to-right columns cor­rect, for a change in these could lead to mis­tak­en use of the wrong col­umn.  In this case, if the tol­er­ances are very tight, con­sid­er­a­tion should be giv­en to have the grain run­ning left-to-right across the page so that any expan­sion in the fibres has an effect top-to-bot­tom rather than left-to-right.

All of these con­sid­er­a­tions seem small in com­par­i­son with machin­ing or the ini­tial lay­out but it’s these small details that will make the final job look and feel bet­ter than one with­out con­sid­er­a­tion of the grain direc­tion.