Polyethylene terephthalate, better known as PET or PETE, is a naturally clear plastic that provides a good boundary against many common liquids while minimizing the absorption of plastic residuals into the liquid. As a result, it is widely used to manufacture beverage bottles, such as those used for soft drinks and bottled water.

In the bottling industry, a very common marking application is recording simple date codes and batch numbers. High throughput speed is required due to the large volume of bottles being processed; however, the marks must also be clearly readable. The standard 10.6-µm CO₂ laser wavelength creates a semi-transparent mark with some clear melt-over. While this mark can be easily read close-up, it becomes less visible from a distance. On the other hand, the less frequently used 9.3-µm CO₂ wavelength is better absorbed by the PET material and thus produces a higher contrast mark that is easily read close-up and at a distance.

To compare PET's absorption behavior, two identical Flyer marking heads equipped with 200 mm focal length lenses were attached to a 10.6-µm wavelength laser and a 9.3-µm wavelength Firestar v30 laser. The focused spot size of the 10.6 µm marking setup was 290 µm (0.011") and the 9.3 µm marking setup produced a spot size of 255 µm (0.010"). Both Flyer heads were controlled by our WinMark Pro laser marking software configured using identical mark file parameters of 3 mm (0.12") high stroke text marked at a scan speed (Velocity) of 1905 millimeters per second (75 ips). The only difference was the duty cycle percentage (Power), which was individually set so each laser produced 18 W of output power.