What characteristic makes a balloon dirigible?

A balloon dirigible is characterized by its ability to be directionally controlled, which distinguishes it from a standard balloon. A dirigible, or airship, is equipped with a propulsion system and control surfaces that allow it to maneuver through the air, making it possible to change direction and altitude. This capability is essential for navigation and transport purposes, enabling the dirigible to follow specific flight paths rather than just being subject to prevailing winds.

The other characteristics listed, such as carrying cargo, being filled with helium, or having a rigid structure, are features that can apply to some dirigibles but do not define them. While many dirigibles can indeed carry cargo and may use helium as a lifting gas, these elements do not inherently contribute to the dirigible's ability to control its flight path. Additionally, some dirigibles have a non-rigid structure, which shows that not all dirigibles possess a rigid frame. Thus, the true defining characteristic is the capability for directional control.