Selection Guide: Gold vs. Polyimide – At Which Temperature Point Must Your Project Choose Gold-Coated Fiber?

In the field of extreme environment sensing and communication, the temperature resistance of the optical fiber is key to system success. There are two main types of high-temperature specialty fibers on the market: Polyimide (PI) Fiber and Gold-Coated Fiber.

A frequent question from customers is: Which one does my project actually need? When is polyimide fiber insufficient, and when must I upgrade to gold-coated fiber?

[Beijing Dacheng Yongsheng Technology Co., Ltd. (DCYS)], as a manufacturer of high-reliability specialty fibers, provides you with a clear selection guide to help you strike the optimal balance between cost and performance.

I. The Polymer Limit: Application Range of Polyimide Fiber (PI)

OFSCN® Polyimide Fiber is the cost-effective high-temperature solution. Its main characteristics and temperature limits are as follows:

• Temperature Range: The stable operating temperature limit is 350°C.
• Performance Characteristics: PI coating offers excellent solvent resistance and mechanical strength. It provides performance far superior to standard fiber in high-temperature, dry, or humid environments below 350°C.
• Applicable Scenarios: Automotive engine compartments, medium-temperature industrial furnaces, general aerospace zones, and most downhole or industrial sensing applications where cost is a consideration.

II. The Metal Limit: The Necessity of Gold-Coated Fiber

OFSCN® Gold-Coated Fiber is specifically designed to challenge the temperature and environmental limits that PI coating cannot reach. It is not just a simple upgrade but a technological leap.

1. The Critical Temperature Decision Point

Core Principle: When your maximum long-term or short-term operating temperature consistently exceeds 350°C, you must choose gold-coated fiber.

Temperature Range	Recommended Choice	Reason
Less than 350°C	Polyimide Fiber (PI)	Best cost-effectiveness and reliable performance.
Greater than 350°C	Gold-Coated Fiber	PI coating risks decomposition. Gold coating provides stable operation guaranteed up to 650°C to 700°C.
Cryogenic Temperatures (Below -200°C)	Gold-Coated Fiber	Gold fiber withstands temperatures down to -269°C, making it the only choice for low-temperature physics and aerospace cryogenic fuel systems.

2. Non-Temperature Factors Requiring Mandatory Selection

Beyond temperature, in certain extremely harsh environments, even if the temperature is below 350°C, you should be required to choose gold-coated fiber to ensure long-term reliability:

• Extreme Hydrogen-Rich Environments: Silica glass fiber suffers hydrogen darkening in high-temperature (e.g., above 200°C) and high-concentration hydrogen (H₂) environments. The gold coating provides a complete Hermetic Seal, which definitively prevents hydrogen gas penetration, making it the most effective means to eliminate hydrogen darkening.
• High Pressure, High Humidity, and Non-Maintainable: The gold coating permanently eliminates static fatigue (hydrolysis), guaranteeing that the fiber will not suffer hydrolytic fracture in humid, high-pressure environments during a service life of 10 years or more.
• Highest Level of Reliability Requirements: Mission-critical applications in core aerospace systems and nuclear industries where the tolerance for failure is 0.

III. Key Performance Comparison Table

The table below summarizes the critical differences between gold-coated and polyimide fibers for selection decisions:

Performance Metric	OFSCN® Polyimide Fiber	OFSCN® Gold-Coated Fiber
Max Temperature Resistance	350°C	700°C
Min Temperature Resistance	-200°C	-269°C
Coating Type	Polymer (Carbon Coating optional)	Metal (Gold)
Hermeticity	Achievable with carbon coating	Inherent Hermeticity (Highest Level)
Hydrogen Darkening Risk	Exists (unless carbon-coated)	Eliminated
Long-Term Corrosion	Good Resistance	Excellent (Inert Metal)
Typical Application	Medium-temp furnaces, Engine compartments	Turbines, Geothermal Wells, Cryogenic Labs

Conclusion: Choose the Right Limit, Save Unnecessary Costs

The selection of specialty fiber should follow the principle of "optimal sufficiency":

1. If your temperature limit is 350°C or below, and hydrogen darkening risk is manageable, choose Polyimide fiber for the best cost-effectiveness.
2. If your temperature exceeds 350°C, or your system operates in extremely harsh high-hydrogen / cryogenic / ultra-high reliability environments, Gold-Coated fiber is your only, irreplaceable choice.

Please contact our expert team. We will provide the most professional selection advice for gold-coated or polyimide fiber based on your actual working conditions and budget.

[Beijing Dacheng Yongsheng Technology Co., Ltd. (DCYS)]

Official Website: https://www.ofscn.org

Product Link (Gold-Coated Fiber): https://www.ofscn.org/optical-fibers/gold-coated.html

Product Link (Polyimide Fiber): https://www.ofscn.org/optical-fibers/polyimide-coated-mm-300.html