Carbon-free paper or NCR paper roll means the paper roll used in the radio to record the details of the register, mainly used to provide customers with a detailed list of shopping, it can be replaced after use. The general material of carbon-free cash register paper is made of a material suitable for internal printing parts of the radio, for an ordinary needle printer, it can be printed with ordinary 1-3 layers of printing paper, for a thermistor printer, it can only be printed with thermosensitive printing paper. 

Classification of cash register paper: 

1. Double rubber paper: Each cash register paper produced by processing ordinary double rubber paper is a monolayer, there is no coating on the paper, and the cash register paper is printed by the ribbon. 

2. Heat-sensitive paper: All cash register paper produced using thermistor paper are all monolayer, the paper is coated with 
thermosensitive chemical coatings, the paper of cash register 
the paper is printed to display color by laser thermosensitive head, its characteristic is not used printing consumables, no carbon tape, ribbons or ink cartridges,  and the surface of the paper is more smooth, with nails or hard objects on the paper scratching will have a clear mark;

3. Self-sensing paper: This kind cash register paper consists of one or more layers, which can be printed to display under the pressure of a printer, printing paper does not need to install ribbon, The first copy of this kind of total cash register paper is called self-sensing paper, and the following ones are common carbon-free paper; 

4. Carbon-free paper: This kind of cash register paper is less made up of two or more layers, the first of them is really to display color by printing machine, but the following ones are really to display color by printing pressure.