SEDs of undetected low-mass TTS with stringent upper limits. Photometry detections are marked as circles, with upper limits marked as inverted triangles. The spectra correspond to Spitzer/IRS observations, when available. For comparison, a photospheric MARCS model (Gutafsson et al. 2008) with a similar spectral type is shown for each object (dotted line). See Table 3 for details regarding the photometry data.