Examples of filaments that correlate with GLIMPSE bubbles. In the upper panel we show an example of the filament tracing the dense material around the periphery of the H ii region; upper middle shows the filament running through the centre of a bubble; lower middle panel shows a filament weaving round two bubbles; lower panel shows a filament that is tracing a section of a much more extended bubble. For image details see caption of Fig. 4.