  Coronal holes are large-scale structures in the solar atmosphere that feature
a reduced temperature and density in comparison to the surrounding quiet Sun
and are usually associated with open magnetic fields. We perform a differential
emission measure analysis on the 707 non-polar coronal holes collected in the
Collection of Analysis Tools for Coronal Holes (CATCH) catalog to derive and
statistically analyze their plasma properties (i.e. temperature, electron
density, and emission measure). We use intensity filtergrams of the six coronal
EUV filters from the \textit{Atmospheric Imaging Assembly} onboard of the
\textit{Solar Dynamics Observatory}, which cover a temperature range from $
\approx 10^{5.5}$ to $10^{7.5}$\,K. Correcting the data for stray and scattered
light, we find that all coronal holes have very similar plasma properties with
an average temperature of $0.94 \pm 0.18$ MK, a mean electron density of $(2.4
\pm 0.7) \times 10^{8}$\,cm$^{-3}$, and a mean emission measure of $(2.8 \pm
1.6) \times 10^{26}$\,cm$^{-5}$. The temperature distribution within the
coronal hole was found to be largely uniform, whereas the electron density
shows a $40\,\%$ linear decrease from the boundary towards the inside of the
coronal hole. At distances greater than \SI{20}{\arcsecond} ($\approx 15$\,Mm)
from the nearest coronal hole boundary, the density also becomes statistically
uniform. The coronal hole temperature may show a weak solar cycle dependency,
but no statistically significant correlation of plasma properties to solar
cycle variations could be determined throughout the observed time period
between 2010 and 2019.
