Loose-tube vs. tight-buffered fibre optic cable

There are two styles of fibre optic cable construction: loose tube and tight buffered. Both contain some type of strengthening member, such as aramid yarn, stainless steel wire strands, or even gel-filled sleeves. But each is designed for very different environments.

Loose-tube cables, the older of the two cable types, are specifically designed for harsh outdoor environments. They protect the fibre core, cladding, and coating by enclosing everything within semi-rigid protective sleeves or tubes. In loose-tube cables that hold more than one optical fibre, each individually sleeved core is bundled loosely within an all-encompassing outer jacket.

Many loose-tube cables also have a water-resistant gel that surrounds the fibres. This gel helps protect them from moisture, so the cables are great for harsh, high-humidity environments where water or condensation can be a problem. The gel-filled tubes can expand and contract with temperature changes, too.

But gel-filled loose-tube cables are not the best choice when cable needs to be submerged or where it’s routed around multiple bends. Excess cable strain can force fibres to emerge from the gel.

Tight-buffered cables, in contrast, are optimized for indoor applications. Because they’re sturdier than loose-tube cables, they‘re best suited for moderate-length LAN/WAN connections, long indoor runs, and even direct burial. Tight-buffered cables are also recommended for underwater applications.

Instead of a gel layer or sleeve to protect the fibre core, tight-buffered cables use a two-layer coating. One is plastic; the other is waterproof acrylate. The acrylate coating keeps moisture away from the cable, like the gel-filled sleeves do for loose-tube cables. But this acrylate layer is bound tightly to the plastic fibre layer, so the core is never exposed (as it can be with gel-filled cables) when the cable is bent or compressed underwater.

Tight-buffered cables are also easier to install because there’s no messy gel to clean up and they don’t require a fan-out kit for splicing or termination. You can crimp connectors directly to each fibre.

Want the best of both worlds? Try a hybrid breakout-style fibre optic cable, which combines tight-buffered cables within a loose-tube housing.

Learn more:
How fibre is insulated for use in harsh environments.