The technological difference between offset printing versus digital printing is in the way the images get transferred onto the paper.
Offset printing uses etched plates that apply ink onto a sheet of paper. The setup for offset printing is generally significantly more time consuming and expensive than digital printing. The metal plates—one plate per each color being used, are chemically etched. Each plate is then applied to the rollers that transfer the ink onto the paper.
Digital printing uses electrostatic rollers—called “drums”—to apply dry toner onto the paper. The drums, one per each color, use an electrostatic charge that attracts toner in the form of toner density. The toner is then applied onto the sheet and then fused—passed through a high-heat unit—onto the paper.
Digital printing can easily print out one sheet of paper or a copy of a booklet and other finishing options inline with less setup than offset. While offset printing requires a considerable amount more setup time and material, the ink and each sheet of paper that comes off of an offset press is actually cheaper than that of a digital press. Making digital printing ideal for short runs, booklets, catalogs or things you need fast!
The number of copies that counts; not the total number of sheets. Offset only makes sense if making a few thousand copies of the same sheets. So for example, if you’re printing 500 copies of a catalog that is 100 pages long, you’re printing 50,000 pages but only 500 copies. This would qualify as “short run printing”. (Offset doesn’t make sense because each sheet would require its own plate to be made.)
Most businesses today doing frequent, quick, and constantly changing print content opt for digital printing. On the other hand—businesses that print in volume and don’t change their content frequently opt for offset printing.
So again—the volume of printing is a key difference between offset printing versus digital printing.