  The circumstellar disk of PDS 70 hosts two forming planets, which are
actively accreting gas from their environment. In this work, we report the
first detection of PDS 70 b in the Br$\alpha$ and $M'$ filters with VLT/NACO, a
tentative detection of PDS 70 c in Br$\alpha$, and a reanalysis of archival
NACO $L'$ and SPHERE $H23$ and $K12$ imaging data. The near side of the disk is
also resolved with the Br$\alpha$ and $M'$ filters, indicating that scattered
light is non-negligible at these wavelengths. The spectral energy distribution
of PDS 70 b is well described by blackbody emission, for which we constrain the
photospheric temperature and photospheric radius to $T_\mathrm{eff}=1193 \pm
20$ K and $R=3.0 \pm 0.2$ $R_\mathrm{J}$. The relatively low bolometric
luminosity, $\log(L/L_\odot) = -3.79 \pm 0.02$, in combination with the large
radius, is not compatible with standard structure models of fully convective
objects. With predictions from such models, and adopting a recent estimate of
the accretion rate, we derive a planetary mass and radius in the range of
$M_\mathrm{p}\approx 0.5-1.5$ $M_\mathrm{J}$ and $R_\mathrm{p}\approx 1-2.5$
$R_\mathrm{J}$, independently of the age and post-formation entropy of the
planet. The blackbody emission, large photospheric radius, and the discrepancy
between the photospheric and planetary radius suggests that infrared
observations probe an extended, dusty environment around the planet, which
obscures the view on its molecular composition. Finally, we derive a rough
upper limit on the temperature and radius of potential excess emission from a
circumplanetary disk, $T_\mathrm{eff}\lesssim256$ K and $R\lesssim245$
$R_\mathrm{J}$, but we do find weak evidence that the current data favors a
model with a single blackbody component.
