Loose-tube optical fiber cable may require _____ tubing to build up the fiber strand's diameter to allow direct connectorization.

Loose-tube optical fiber cable often features fibers that are protected by a flexible tube which allows them to expand and contract with temperature changes without damaging the fiber itself. However, when it comes to preparing these fibers for direct connectorization, the fibers themselves may be too thin to fit properly into standard connectors designed for a certain diameter.

Furcation tubing, which is the correct answer, is used to cover and build up the diameter of the individual optical fibers. It serves as a protective layer while also providing the necessary thickness to ensure that the fibers can be effectively integrated with connectors or distribution frames. Furcation tubing also maintains the mechanical strength of the fibers and protects them from external stresses and environmental factors.

The other options are not suitable in this context. Connector refers to the device that joins the fiber to another fiber or a piece of equipment, insulation typically relates to protecting wires from electrical interference, and cable refers to the entire assembly that includes the fiber strands. None of these serve the specific purpose of increasing the diameter of the fiber strand for connectorization like furcation tubing does.