Barcode Direct Thermal Label 2″ X 1″ – They are direct thermal labels with 1000 in each row. Inner core is 4 cm and the outer core is 7.5 cm. Direct thermal labels usually made by thermal print head to selectively heat specific areas of coated, thermo-chromatic paper. The heat sensitive media / paper blackens in the heated area when it runs over the thermal print head. Thermal transfer printing involves heated ribbon which produces durable images on a wide range of materials.