Plastic Classification and Inspection since the plastic material is permeable at infrared wavelength, the interior of the plastic cannot be seen by eye, but can be examined by infrared. Infrared examination is used to detect materials such as metal, liquid remaining in plastic packaging or coating. For example, the height of liquids such as fruit juice, milk, detergent in non-transparent plastic boxes in the production line can be seen and the amount can be determined.

In the example picture, the metal RF parts inside the identity document are easily visible in the SWIR spectrum.