  We investigate the increase of the DEM (differential emission measure)
towards the chromosphere due to small and cool magnetic loops (height
$\lesssim8$~Mm, $T\lesssim10^5$~K). In a previous paper we analysed the
conditions of existence and stability of these loops through hydrodynamic
simulations, focusing on their dependence on the details of the optically thin
radiative loss function used. In this paper, we extend those hydrodynamic
simulations to verify if this class of loops exists and it is stable when using
an optically thick radiative loss function. We study two cases: constant
background heating and a heating depending on the density. The contribution to
the transition region EUV output of these loops is also calculated and
presented. We find that stable, quasi-static cool loops can be obtained by
using an optically thick radiative loss function and a background heating
depending on the density. The DEMs of these loops, however, fail to reproduce
the observed DEM for temperatures between $4.6<\log T<4.8$. We also show the
transient phase of a dynamic loop obtained by considering constant heating rate
and find that its average DEM, interpreted as a set of evolving dynamic loops,
reproduces quite well the observed DEM.
