Polystyrene films are used to provide superior calibration using radially symmetric films which eliminates the effects of the extruded film. The films come in a pair of two, each with different thickness and differential absorbance intensities. The films are mounted on a 2 X 4 cardstock holder and comes with a certificate of traceability to five NIST 1921b frequencies. The polystyrene coating prevents the damage to KBr window from moisture.