Dust models for HD 027778 (left), HD 108927 (middle), and HD 287150 (right). For each sightline we show, from top to bottom, the reddening curve, the optical polarisation spectrum, and the total and polarised (I and P) dust-emission spectrum. The reddening-curve data with error bars are described in the text. The observed starlight polarisation is shown for the unbinned spectrum (grey lines) and for data binned to a spectral resolution of λ/Δλ ~ 50 (black circles). The dust emission is consistent with Planck 353 GHz measurements (filled circles). Model curves with the adopted a/b ratio and porosity (V) are indicated in the legend. The individual contributions to the observables are shown for nanoparticles (green), amorphous carbon grains (brown), silicates (orange), and micrometre-sized agglomerates (grey shading) for the best-fit model with the parameters listed in Table 2.