You should never feed sheets into a printer against the grain - here's the reasons why.
What does "against the grain" mean?
It’s all to do with how paper is made; paper is made up of many, many, many (many) tiny threads or “fibres” of cellulose. During the manufacturing process, these fibres will end up lying in a common direction (usually parallel with the direction of the web (the continuous roll of material that paper is made into) through the machine). The direction that the majority of the fibres lie in is called the “grain”. When the large web is cut down into individual sheets of paper, the fibres will either be parallel with the longest edge of the sheet (known as long-grain or grain-long) or the shortest edge of the sheet (known as short-grain or grain-short).
Paper used for printing and label making is commonly cut so that the grain runs parallel with the longest edge; i.e. when the sheet is held portrait, the grain runs from the top of the sheet to the bottom (and from the bottom to the top!).
So why is the grain important?
Paper is strongest and most stable with the grain; for example, if you fold a sheet of paper with the grain, you get a smooth, effective fold, whereas a fold against the grain will result in the paper “springing” back open or cracking along the fold. Similarly, if you tear a sheet of paper with the grain you will find that the edges are clean and straight, while a tear against the grain results in ragged, uneven edges.
When a sheet of paper (or a sheet of paper labels) is fed through a printer, it is pulled through and around a series of rollers, which creates tension in the sheet and it is this that can cause problems if the sheet is fed into the printer against the grain. Attempting to feed a sheet through a printer against the grain can result in poor print results or in the sheet jamming within the printer. If you are printing labels, this can have the added consequence of causing some or all of the labels to begin peeling off the backing sheet, while still inside the machine.
So, you should always feed your labels into your printer with the sheet in a PORTRAIT orientation, so that the NARROW EDGE (210mm) enters the printer first, and the sheet is fed through the printer in the direction of/WITH THE GRAIN.
[It should be noted that SOME manufacturers may produce labels and other paper products where the grain lies parallel with the shortest edge of the sheet. This is more commonly found when the finished sheet is of a larger size than A4 (and the sheet may be either long-grain or short-grain); manufacturers will indicate the grain on the packaging, so that you can check this for yourself. At Label Planet, however, all of our products are cut long-grain, so they should ALWAYS be fed into a printer NARROW EDGE leading.]