Clues and Knowhow: Office Paper: Clue No. 2: Print on proper side
Good office papers have an initial tension or swell, to respond to the forces acting inside a laser printer, like pressure and heat. Eventually the pages end up in the paper tray without any kind of deformation.
If you print onto the wrong side of the sheet, swell can aggravate and creases can occur.
Good office papers bear a mark (picture right side) and show you, which side of the sheet to print on first.