The integrating sphere is a device that coupled with the FTIR allows determining optical properties of materials such as absorptivity, reflectivity, and transmissivity at a different wavelength.

The beam of the FTIR passes mid-infrared wavelength radiation through the integrating sphere with a sample attached to it. Then, radiation reflected by and transmitted through the tested material is quantified and optical properties determined. The integrating sphere can be used with a DTGS or an MCT detector, providing different range of accuracy and sensitivity.

Optical properties of materials in the mid-infrared are key to develop accurate heat transfer and pyrolysis models for materials under conditions of severe heat exposure from fires. The use of this device allows to significantly decrease the uncertainty in fire testing, especially when using radiant devices such as the Cone Calorimeter, the Fire Propagation Apparatus, or the modular array of radiant panels.