Surface brightness I_ν of the main astrophysical components of the submm and mm sky at high Galactic latitude, i.e., Galactic cirrus, CIB fluctuations, and CMB anisotropies. Typical SEDs of sources at intermediate and high redshift, i.e., z = 1–4, are modelled by a modified blackbody emission law (with T_xgal = 30 K and β_xgal = 1.5) and plotted in colours, from blue (z = 1) to red (z = 4). The ±2σ levels of Galactic cirrus and CIB fluctuations are shown as light and dark grey shaded areas, respectively. The bandwidths of the 3 THz IRIS and the six Planck-HFI bands are shown as light grey vertical bands.