  Spherically symmetric expansionfree distributions are systematically studied.
The whole set of field equations and junction conditions are presented for a
general distribution of dissipative anisotropic fluid (principal stresses
unequal), and the expansionfree condition is integrated. In order to understand
the physical meaning of expansionfree motion, two different definitions for the
radial velocity of a fluid element are discussed. It is shown that the
appearance of a cavity is inevitable in the expansionfree evolution. The
nondissipative case is considered in detail and the Skripkin model is
recovered.
