Behaviour of non-C₂ DIBs 115780 and 6196 (left panels), and C₂ DIBs 114963 and 4984 (right panels) in C₂ and non-C₂ sightlines. The non-C₂ DIBs show the ‘skin effect’ and have reduced strengths in the C₂ sightlines. However, the behaviour of the C₂ DIBs is rather similar in the two types of sightlines. They may trace deeper regions of a cloud than the non-C₂ DIBs, but not as deep as the C₂ molecules. The DIB equivalent width data are gathered from Fan et al. (2017).