The movement of infrared radiation through an object is called transmission.
Most objects are impermeable to infrared radiation.
Therefore the proportion of transmission is usually set to zero, if the object is measured by an infrared camera.
Exceptions are thin plastic films. Here transmission occurs. An infrared measurement of a thin film usually shows the surface temperature of the underlying object and not the one from the film.
Related topics:
IR Temperature Measurement
This glossary of plastic industry is provided by PLEXPERT Canada Inc.