Sheathe fiber optic bundles comprised of individual strands as small as 25µm in diameter. Sheathing has three core values for use in fiber optic design: Protect the fiber. Keep ambient or stray light from creating signal noise (for sensor applications). When individual fibers break, light transmission and uniformity. In reality, cable sheath selection has a direct impact on fire safety, outdoor durability, installation flexibility, and long-term maintenance cost. Choosing the wrong sheath material may not cause immediate failure, but it often leads to accelerated aging, regulatory issues, or repeated field. The sheathing process is where you apply the final touch to your loose tube fiber optic cable. Understand the Environmental.