  The evolution of a supernova remnant in a cloudy medium as a function of the
volume filling factor of the clouds is studied in a three-dimensional axially
symmetrical model. The model includes the mixing of heavy elements (metals)
ejected by the supernova and their contribution to radiative losses. The
interaction of the supernova envelope with the cloudy phase of the interstellar
medium leads to nonsimultaneous, and on average earlier, onsets of the
radiative phase in different parts of the supernova envelope. Growth in the
volume filling factor $f$ leads to a decrease in the time for the transition of
the envelope to the radiative phase and a decrease in the envelope's mean
radius, due to the increased energy losses by the envelope in the cloudy
medium. When the development of hydrodynamical instabilities in the supernova
envelope is efficient, the thermal energy falls as $E_t\sim t^{-2.3}$, for the
propagation of the supernova remnant through either a homogeneous or a cloudy
medium. When the volume filling factor is $f\simgt 0.1$, a layer with excess
kinetic energy andmomentumforms far behind the global shock front from the
supernova, which traps the hot gas of the cavity in the central part of the
supernova remnant. Metals ejected by the supernova are also enclosed in the
central region of the remnant, where the initial (high) metallicity is
essentially preserved. Thus, the interaction of the supernova envelope with the
cloudy interstellar medium appreciably changes the dynamics and structure of
the distribution of the gas in the remnant. This affects the observational
characteristics of the remnant, in particularly, leading to substantial
fluctuations of the emission measure of the gas with $T>10^5$~K and the
velocity dispersion of the ionized gas.
