Direct Thermal

Direct thermal labels react to heat and turn black.  When they are put through a Direct thermal printer the image is printed on the labels using heat ie without needing ink.  This makes direct thermal labels easy to use and reasonably low cost.
Thermal labels do not last as long as labels printed using inks.  They turn brown with heat so if they are left in the sun they turn black.  Also - thermal labels increase the wear on the printer's printhead, so the printers head needs replacing more frequently.
Where you want to avoid the inconvenience of ink ribbons and the life of the labels is short, thermal labels are the best option.