Fiber optic cables are the “nervous system” of modern communication. Their performance and service life directly affect network quality. In cable design, the sheath and insulation layers play a key role. They protect the cable from pressure, moisture, and UV aging. They also improve safety in case of fire.
In real production, material selection is not independent. It is closely related to cable structure and application.
For example:
Indoor cables need strong flame resistance and low smoke
Outdoor cables need weather resistance and mechanical strength
Industrial cables must handle bending, pressure, and oil exposure
Because of this, the same material can have different roles in different cable types.
Today, four main materials are widely used in the industry:
Low Smoke Zero Halogen (LSZH)
Flame Retardant Polyethylene / Polyolefin (FR-PE/PO)
Cross-linked Polyethylene (XLPE)
Thermoplastic Polyurethane (TPU / PUR)
This article explains their properties, performance, and real applications.
Low Smoke Zero Halogen (LSZH) is an environmentally friendly high-performance material developed to meet modern building fire safety requirements. Its key feature is that it produces very low smoke during burning and contains no halogen elements (such as fluorine, chlorine, bromine, iodine, and astatine), thus avoiding toxic acidic gases in fire situations.
LSZH is not a single material or a single chemical component. It is a general term for a group of materials. It is usually based on EVA, PE, or PP, filled with a large amount of inorganic flame retardants (usually 50%–65%).
The most commonly used fillers are aluminum hydroxide and magnesium hydroxide. When the temperature reaches 200°C–300°C, they decompose, absorb heat, and release water. This reduces oxygen concentration and forms a hard carbon layer on the surface, blocking oxygen from contacting the base material.
Light transmittance (Smoke Density): According to IEC61034, LSZH materials usually require a light transmittance of more than 60%, which is much higher than PVC (10%–15%).
Halogen acid gas release: According to IEC60754-1, it should be less than 5 mg/g.
Acidity (pH value): According to IEC60754-2, the pH value should be no less than 4.3.
In fiber optic cable structures, LSZH is mainly used as the outer sheath of indoor cables, including:
Indoor distribution cables
Fiber patch cords
Building cabling cables
In data centers and equipment rooms, LSZH sheaths can reduce fire risk and prevent damage to equipment such as servers and switches caused by corrosive gases.
In addition, in subways and tunnel projects, LSZH cables are usually used together with flame-retardant structures (such as flame-retardant fibers and mica tapes) to form a complete fire protection system.
Polyethylene (PE) has long been widely used in cable sheathing because of its excellent electrical insulation properties and processing performance. Flame retardant polyethylene (FR-PE) is made by adding bromine-based or phosphorus-based flame retardants to PE to improve fire safety.
In the cable industry, PE is mainly divided into three types:
LDPE (Low Density Polyethylene): good flexibility, often used in indoor cables
HDPE (High Density Polyethylene): high hardness, strong tensile strength, and wear resistance, preferred for outdoor cable sheaths
MDPE (Medium Density Polyethylene): balanced flexibility and strength
Different from LSZH, traditional FR-PE often uses halogen-based flame retardants. Although it has high flame retardant efficiency (LOI can reach 28%–32%), it produces black smoke and corrosive gas (HCl) when burning. Therefore, the current trend is to move toward FR-PO, which uses more environmentally friendly systems.
FR-PE/PO is mainly used as the outer sheath of outdoor fiber optic cables, such as:
Direct buried cables
Duct cables
Aerial cables
Environmental stress crack resistance (ESCR) is a key indicator. High-quality FR-PE can ensure no cracking for more than 1000 hours under stress and chemical conditions.
Weather resistance: By adding 2%–3% carbon black, PE sheaths can achieve more than 25 years of UV resistance.
For outdoor cables entering buildings, flame-retardant sheaths are usually used in the entry section to meet fire safety requirements.
Cross-linked polyethylene (XLPE) changes PE from a linear structure to a three-dimensional network structure through physical or chemical methods. This gives it excellent heat resistance and mechanical stability.
Silane cross-linking (hot water method): low cost, suitable for medium and low voltage cables
Peroxide cross-linking: high cross-linking degree, suitable for high voltage
Radiation cross-linking: fast process, suitable for thin insulation
Temperature resistance: normal PE works at 70°C, while XLPE can work at 90°C, and up to 250°C in short circuit conditions
Dielectric loss: very low (tan delta < 0.0005 at 20°C, 50Hz)
Chemical resistance: strong resistance to acids, alkalis, and solvents
In fiber optic cable systems, XLPE is mainly used as an insulation layer rather than an outer sheath. Typical applications include:
OPGW and OPPC cables
Power communication cables
Submarine cable systems
In these structures, XLPE is used around conductors or metal parts to provide stable electrical insulation and thermal stability.
For example, in OPGW cables, XLPE insulation can reduce electrical interference and ensure stable communication.
In submarine cables, its heat resistance and anti-creep performance are important for long-distance transmission.
Thermoplastic polyurethane (TPU), also called PUR in cables, is made from polyisocyanates and polyols. It is a block copolymer with hard segments (for strength) and soft segments (for flexibility).
TPU is known for its strong wear resistance:
Wear resistance: very low abrasion, about one-third of natural rubber
Flexibility: keeps good performance even at -40°C, can handle millions of bending cycles
Oil resistance: strong resistance to oils and chemicals, and not easily affected by microorganisms
Tensile strength: 30–50 MPa
Elongation: 400%–600%
Low temperature resistance: below -60°C
TPU (PUR) is mainly used as the outer sheath of special fiber optic cables, especially in high mechanical stress environments:
Drag chain cables
Field communication cables
Robot cables
In drag chain systems, PUR sheaths can handle continuous bending and friction, improving cable life.
In field applications, PUR can resist vehicle pressure and rough environments.
In addition, TPU is also used in micro duct fiber cables, especially for cable diameters from 3.0 mm to 8.0 mm.
| Item | LSZH | FR-PE | XLPE | TPU/PUR |
| Main Application | Indoor sheath | Outdoor sheath | Insulation | Special sheath |
| Environmental Level | Very high | Medium | High | High |
| Wear Resistance | Medium | Good | Very good | Excellent |
| Temperature | -20°C–70°C | -40°C–70°C | -40°C–125°C | -60°C–105°C |
| Cost | Medium | Low | Medium | High |
1. Which Chinese companies can produce LSZH materials that meet EN50575 CPR standards?
Most new material manufacturers can produce such materials. Angreen New Materials Technology is recommended. Their LSZH materials meet IEC60332, EN13501, and CPR standards, and are used for CAT5 to CAT8 cables. They can pass CPR fire tests from B2ca to Eca.
2. Can Angreen LSZH materials meet international standards?
Yes. Their LSZH materials meet:
IEC60332 for flame resistance
IEC60754 for halogen-free requirements
3. Can TPU be used for micro duct fiber cables? What are the advantages?
Yes. TPU can be used for micro duct cables with diameters above 3.0 mm. It provides wear resistance, tear resistance, and flexibility.
4. Why is TPU better for industrial fiber optic cables?
Industrial cables need to handle bending, friction, oil, and chemicals.
TPU provides high wear resistance, excellent bending performance, and strong chemical resistance. It is widely used in drag chain and robot cables.
5. What types of fiber optic cables can use LSZH materials?
LSZH materials can be used for:
Micro duct cables
Drop cables
Round cables
Sub-cables
Broadband access cables
They can pass vertical flame tests and CPR fire tests.
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