There are two types of thermal printing.
Direct Thermal technology prints onto heat-sensitive paper. A printhead consisting of a series of resistors generates pulses of heat which develop an image through a chemical reaction with the paper. Direct Thermal paper is available in different grades and sensitivities to match application requirements. In general Direct Thermal is mainly used for short-term applications. Direct exposure to both high temperatures and UV light should be avoided.
Thermal Transfer technology generates heat that is applied to an inked ribbon that transfers ink onto the substrate. The ribbon is made of thin film on which a mixture of ink with wax and/or resin is applied. This mixture, solid at room temperature and liquid when heated, is transferred onto the substrate. Unlike the Direct Thermal process, no chemical reaction takes place. Therefore, Thermal Transfer can print on a variety of substrates, such as paper, polypropylene, fabric, PVC, plastic, and many others.
Both technologies are available with either flat-head or near-edge printheads. Common resolutions are 200 and 300 dpi.