Products Description
What Is a Water Blocking Yarn?
A water blocking yarn is a swellable yarn used inside cables to stop water from travelling along the cable. It is made of polyester industrial filament composited with a cross-linked polyacrylic super absorbent material.
When water enters a cable protected by water blocking yarns, the super-absorbent component within the yarn instantly forms a water blocking gel, and the yarn swells to approximately three times its dry size, sealing the space it occupies.
Water blocking yarns are used in optical, copper telephone, data and power cables as cable components. They serve three jobs inside the cable:
Water blocking - sealing the interstices against lengthwise water migration.
Binding - bundling and holding cable components together.
Filling - occupying the gaps between components so the cable core is compact and water has nowhere to travel.
How It Works
Dry state - the yarn is a thin, flexible cord laid, stranded or served along the cable.
Water contact - the super absorbent material absorbs water and forms a gel.
Swelling - the yarn expands to roughly 3× its dry size, filling the interstice it sits in.
Blocking - the swollen yarn seals the water path at the point of entry, preventing migration.
Its swelling behaviour is graded by two measures:
Swelling speed - how fast the yarn absorbs in the first minute (ml/g/1 min).
Swelling capacity - how much it absorbs at full swell (ml/g).
Water Blocking Yarn vs. Water Blocking Tape
Yarn and tape are complementary, not substitutes: the tape is a flat sheet that wraps the cable core as a continuous barrier; the yarn is a thin cord that fills the gaps and interstices inside the cable. Many cables use both - the tape as the outer barrier, the yarn to block the internal spaces.
Specifications
Standard water blocking yarn (ZS series)
| Model | Denier (D) | Linear density (m/kg) | Swelling speed (ml/g / 1 min) | Swelling capacity (ml/g) | Tensile strength (N) | Elongation at break (% min) | Moisture content (% max) |
|---|---|---|---|---|---|---|---|
| ZS-1.0 | 9000 | 1000 | 50 | 60 | 250 | 10 | 8 |
| ZS-2.0 | 4500 | 2000 | 45 | 60 | 150 | 10 | 8 |
| ZS-3.0 | 3000 | 3000 | 45 | 50 | 100 | 10 | 8 |
| ZS-4.5 | 2000 | 4500 | 40 | 50 | 70 | 10 | 8 |
| ZS-5.0 | 1600 | 5000 | 35 | 45 | 60 | 10 | 8 |
| ZS-6.0 | 1500 | 6000 | 30 | 40 | 50 | 10 | 8 |
| ZS-10.0 | 900 | 10000 | 20 | 30 | 20 |
SAF water blocking yarn
| Specification | Description | Unit weight (g/100 m) | Tensile strength (N) | Swelling speed (ml/g × 1 min) | Swelling capacity (ml/g) |
|---|---|---|---|---|---|
| SA01 | 1000 m/kg absorbent-fiber filler cord, SAF water blocking yarn | 100 | 55 | 40 | 45 |
| SA02 | 1250 m/kg absorbent-fiber filler cord, SAF water blocking yarn | 80 | 58 | 40 | 45 |
| SA03 | 2000 m/kg absorbent-fiber filler cord, SAF water blocking yarn | 50 | 50 | 45 | 50 |
| SF01 | 36000 m/kg absorbent-fiber filler cord, SAF water blocking yarn | 3.3 | 3 | 28 | 35 |
| SF02 | 15000 m/kg absorbent-fiber filler cord, SAF water blocking yarn | 6.6 | 7 | 28 | 35 |
Reading the tables: the ZS series runs from a heavy, high-strength yarn (ZS-1.0, 250 N) for larger voids to a fine, high-metreage yarn (ZS-10.0, 20 N) for tight spaces. Higher-denier yarns give more strength; higher-metreage (lower-denier) yarns fill finer gaps and cover more length per kilogram.
Customization & Ordering
To quote a cable water blocking yarn, confirm:
Series - ZS or SAF.
Model / denier - from the tables above, or a specified linear density.
Swelling requirement - required swelling speed and swelling capacity.
Tensile requirement - minimum breaking strength for the application.
Package - bobbin or cone type and net weight.
Cable type and quantity - the target cable construction and order volume.
Because the yarn is manufactured to the confirmed specification, model, denier and quantity are confirmed per order. Send your requirement and we will confirm feasibility, MOQ and lead time.
Request a Quotation
Tell us your cable type (optical fiber, copper telephone, data or power), the void you need to fill, and the required swelling and strength performance. We will recommend the matching water blocking yarn and confirm MOQ and lead time for your order.
Optical cable water-blocking material fiber forming production line in workshop
FAQ
What is water blocking yarn made of? Polyester industrial filament composited with a cross-linked polyacrylic super absorbent material.
How much does it swell? To approximately three times its dry size on water contact.
Where is water blocking yarn used? In optical, copper telephone, data and power cables - inside loose tubes, around fiber bundles and in the interstices between core components.
What is the difference between using and not using it? Without it, water entering the cable travels freely along its length and turns a local defect into a long-length repair. With it, the yarn gels and swells to block the water path at the point of entry, confining the damage and extending cable life.
What is the difference between water blocking yarn and water blocking tape? The tape wraps the cable core as a continuous barrier; the yarn fills the gaps and interstices inside the cable. They are complementary and often used together.
Can I get a custom denier or swelling performance? Yes - model, denier, swelling performance and packaging are built to order.
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