Average 6.9 µm profile based on 24 spectra with a 3σ detection of this band (red). The envelope on the average feature represents a 1σ variation in the profile. The individual 6.9 µm band profiles of SMP SMC Oil (Class A) and IRAS 05341 (Class undetermined) (top), Class B (middle) and Class D (bottom) are shown in grey-scale. For Class B, a representative sample is shown for clarity. The band profiles (in Wm⁻² µm⁻¹) were normalised to the fitted peak flux densities of the features.