# Why is there "yellow fuzz" inside the patch cord?

**URL:** <https://forum.ofscn.net/t/why-is-there-yellow-fuzz-inside-the-patch-cord/1629>\
**Category:** OFSCN Technical Knowledge Base\
**Tags:** fbg-technology\
**Created:** [April 8, 2026, 2:15pm UTC](https://forum.ofscn.net/t/why-is-there-yellow-fuzz-inside-the-patch-cord/1629 "2026-04-08T14:15:57Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![frostweaver](https://forum.ofscn.net/letter_avatar_proxy/v4/letter/f/da6949/32.png) [@frostweaver](https://forum.ofscn.net/u/frostweaver)\
**Post date:** [April 8, 2026, 2:15pm UTC](https://forum.ofscn.net/t/why-is-there-yellow-fuzz-inside-the-patch-cord/1629/1 "2026-04-08T14:15:57Z")

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What is the purpose of those hair-like “Aramid yarns” (Kevlar)? Is it okay to cut them off during installation?

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**Author:** ![OFSCN\_Tech\_Expert](https://forum.ofscn.net/user_avatar/forum.ofscn.net/ofscn_tech_expert/32/199_2.png) [@OFSCN\_Tech\_Expert](https://forum.ofscn.net/u/OFSCN_Tech_Expert)\
**Post date:** [April 8, 2026, 2:16pm UTC](https://forum.ofscn.net/t/why-is-there-yellow-fuzz-inside-the-patch-cord/1629/2 "2026-04-08T14:16:02Z")

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The “yellow fuzz” you see inside the fiber optic patch cord is indeed **Aramid yarn** , commonly known by the brand name **Kevlar®**. In the field of fiber optics, particularly regarding the products we manufacture at DCYS (OFSCN), these fibers serve a critical engineering purpose.

### 1. The Purpose of Aramid Yarns

Aramid yarns serve as the **strength members** of the cable. Since the internal glass fiber is extremely fragile and has a very low tolerance for pulling forces, the Aramid yarns are designed to:

- **Provide Tensile Strength:** They absorb the tension when the cable is pulled during installation or handling, preventing the glass fiber from stretching or breaking.
- **Protect the Bend Radius:** They add a layer of structural integrity that helps maintain the cable’s shape and prevents sharp kinks.
- **Provide Cushioning:** They act as a mechanical buffer between the outer jacket and the inner buffered fiber.

### 2. Can you cut them off during installation?

The answer depends strictly on **where** you are cutting:

- **During Connector Termination:** Yes, you **must** trim the Aramid yarn using specialized Kevlar shears so that the fiber can be inserted into the connector ferrule. However, in high-quality terminations, the yarn is often crimped to the connector body to provide “strain relief.”
- **Mid-span (Inside the jacket):**  **No.** You should never cut or remove the Aramid yarns from inside the cable jacket where the cable is still intact. Doing so removes the tensile protection, and even a slight tug on the patch cord could lead to a permanent break in the fiber or significant signal loss.

### 3. Application in FBG Sensors

In the context of **Fiber Bragg Grating (FBG) technology**, mechanical stability is even more vital. Because FBG sensors often operate in harsh environments, we frequently use more robust protection than just Aramid yarn. For example, our sensors often utilize seamless steel tubes for maximum protection.

If you are working with standard patch cords for connecting FBG interrogators or sensors, please ensure the Aramid yarn is properly secured at the connector end to prevent the fiber from pulling out of the ceramic ferrule.

For more technical details on fiber construction and sensor protection, you can refer to our technical resources:

- [OFSCN® Fiber Bragg Grating (FBG) Sensors and Products](https://www.ofscn.net)
- [Specialty Optical Fiber and Cables](https://www.ofscn.org)

If you have questions regarding the specific tensile ratings of our cables or how to properly terminate them for high-temperature FBG applications, feel free to ask.