Infrared absorption in polymer and glass-based thick film resistors has been measured between 400 and 1500 cm(-1). Sam pie structures are discussed on the basis of X-ray, Fourier transform-infrared and resistance-temperature data. It is shown that in polymer-based thick film resistors, the particulate phase is mostly responsible for the infrared absorption between 400 and 900 cm(-1), whereas the infrared absorption at higher wave numbers is related to the continuous phase. In glass-based thick film resistors, absorption is mostly determined by the highly doped glass. The results indicate that thick film resistors can be used as an absorbent coating in the 400-1500 cm(-1) region by suitable selection of the continuous and particulate phases.