An implosion can propel material outward (for example due to the force of inward falling material rebounding, or peripheral material being ejected as the inner parts collapse), but this is not an essential component of an implosion and not all kinds of implosion will do so. If the object was previously solid, then implosion usually requires it to take on a more dense form - in effect to be more concentrated, compressed, denser, or converted into a new material that is denser than the original.
