A rotary printing press is a printing press in which the images to be printed are curved around a cylinder. Printing can be done on various substrates, including paper, cardboard, and plastic. Substrates can be sheet feed or unwound on a continuous roll through the press to be printed and further modified if required (e.g. die cut, overprint varnished, embossed). Printing presses that use continuous rolls are sometimes referred to as "web presses".