What feature differentiates Loose Tube cables from other types?

Loose Tube cables are characterized by having fibers that are housed in a tube that is not tightly bound to the insulation. This design allows the fibers to move freely within the tube, which is critical for accommodating any thermal expansion or environmental shifts. The presence of a buffered fiber with a water-blocking substance is a distinctive feature of Loose Tube cables, as it helps to protect the fibers from moisture ingress and environmental factors. This buffering is essential for maintaining signal integrity and protecting the fibers in various installations.

The other options suggest characteristics that do not accurately represent Loose Tube cables. For instance, being rigid and bulky typically describes other types of cables, while Loose Tube cables are known for their flexibility. Additionally, while Loose Tube might be cost-effective, this is not a defining feature when compared to other cable types. Lastly, the reference to strength members is somewhat contradictory; Loose Tube cables do generally include strength members to provide support and prevent damage but allow enough space within the tube for movement, unlike other designs where fibers may be directly attached to strength members. Therefore, the specific feature of having a buffered fiber with a water-blocking substance stands out as the key differentiator for Loose Tube cables.