Carbon-free printing paper, also named NCR paper roll is generally used in the office, they also need to be classified into office use, the main division of  the classification is based on its size and the number of layers, for example: 241-1 / 241-2,  what they represent is the number of layers of carbon-free printing paper, one layer, two layers, of course, there's a thicker one, common printing paper width has 381-1,381-2, for example: 241-0 means carbon-free printing paper, which is used on a needle printer. Carbon-free printing paper is also called pressure-sensitive printing paper, as long as it is made from the combination of upper and lower paper and medium paper, it is based on the principle of the chemical reaction of acidic clay in the chromogenic layer of the chromogenic agent. While printing, it is mainly by the needle of printing to the product cotton cloth can achieve the effect of color development. Generally, the number of layers of common color rendering is 2-6 layers.