Products Description
What Is a Water Blocking Tape?
A water blocking tape is a swellable tape used inside optical and electrical cables to stop water and moisture from travelling along the cable. It is built from polyester fiber non-woven fabric composited with a super absorbent material. When water enters a cable protected by the tape, the super absorbent powder within it instantly forms a water blocking gel and swells, sealing the gap and preventing further - and far more costly - damage to the cable.
The tape reduces water and moisture ingress, protects the cable core and extends cable service life.
How It Works
Dry state - the tape is a thin, flexible non-woven sheet that wraps around the cable core or between layers.
Water contact - the super absorbent polymer (SAP) in the tape absorbs water and swells rapidly.
Sealing - the swollen tape fills the wrapped layer and blocks water from propagating lengthwise along the cable.
Recovery - the swelling is stable in service; the tape holds its blocking function across the cable's life.
The swelling behaviour is graded by two measures used throughout the specification tables below:
Swelling speed - how fast the tape swells in the first minute (mm/1st min).
Swelling height - how much the tape expands at full swell (mm).
Types and Specifications
Water blocking tapes are supplied in three families, matched to the cable's electrical and construction requirements:
Non-conductive water blocking tape (ZD series) - the standard insulating grade for general cable-core wrapping.
PET laminated water blocking tape (ZDF series) - a PET film laminated onto the tape for added mechanical strength and handling.
Semi-conductive water blocking tape (BZD series) - a conductive grade for power-cable applications where the tape must sit in the cable's electrical field.
Non-conductive water blocking tape (ZD) and PET laminated water blocking tape (ZDF)
| Item | Unit | ZD-20 | ZD-25 | ZD-30 | ZDF-25 | ZDF-30 |
|---|---|---|---|---|---|---|
| Thickness | mm | 0.20 | 0.25 | 0.30 | 0.25 | 0.30 |
| Weight | g/m² | 80 ± 8 | 90 ± 9 | 100 ± 10 | 100 ± 10 | 120 ± 10 |
| Swelling speed | mm / 1st min | 7 | 8 | 10 | 7 | 10 |
| Swelling height | mm | 9 | 12 | 14 | 12 | 14 |
Semi-conductive water blocking tape (BZD)
Application: Be used for shielding and binding in the outside of conductor and inuslation core.With super high strength. It is particularly suitable for shielding, binding and isolating of high voltage and super high voltage cable for splitting conductors.
| Properties | SCT-18 | SCT-20 | SCT-25 |
| Thickness (mm) | 0.18±0.03 | 0.20±0.03 | 0.25±0.03 |
| Weight(g/m2) | 150±20 | 170±20 | 180±20 |
| Tensile strength(N/cm) | ≥ 220 | ≥ 220 | ≥ 220 |
| Elongation(%) | ≥ 25 | ≥ 25 | ≥ 25 |
| Surface resistance Ω | ≤1000 | ≤1000 | ≤1000 |
| Volume resistance (Ω.cm) | ≤1×105 | ≤1×105 | ≤1×105 |
| Short term stability (°C) | 230 | 230 | 230 |
| Long term stability (°C) | 145 | 145 | 145 |
Semi-conductive Cushion water blocking tape
| Item | Unit | BZD-30 | BZD-50 |
|---|---|---|---|
| Thickness | mm | 0.30 | 0.50 |
| Weight | g/m² | 110 | 180 |
| Swelling speed | mm / 1st min | 6 | 12 |
| Swelling height | mm | 12 | 16 |
Physical and mechanical properties (ZD and ZDF types)
| No. | Property | Unit | Value |
|---|---|---|---|
| 1 | Tensile strength | N/cm | ≥ 35 |
| 2 | Elongation at break | % | ≥ 12 |
| 3 | Long-term stability - swell height after 90 °C, 24 h | mm | < initial value |
| 4 | Short-term stability - swell height after 230 °C, 20 s | mm | < initial value |
| 5 | Water content | % | ≤ 9 |
Reading the stability rows: the tape keeps a swell height below its initial (dry-state) value after both long-term heat aging (90 °C, 24 h) and short-term high heat (230 °C, 20 s) - the swelling behaviour is retained through the cable's processing and service temperatures.
Water Blocking Tape vs. Water Blocking Yarn
Both are swellable water-blocking materials, but they work in different places and different ways. They are often used in the same cable, filling different gaps.
The core difference: a water blocking tape is a flat sheet that wraps the cable core and forms a continuous barrier; a water blocking yarn is a thin cord that fills the gaps and interstices inside the cable, blocking water in spaces a tape cannot reach.
| Aspect | Water Blocking Tape | Water Blocking Yarn |
|---|---|---|
| Form | Flat, continuous sheet on rolls (0.20–0.50 mm thick) | Thin, round/stranded cord |
| Base | Polyester non-woven + super absorbent polymer (PET-laminated for ZDF) | Super-absorbent / SAP-blended yarn |
| Placement | Wrapped or overlapped around the cable core or between layers | Stranded, served or laid longitudinally inside the cable |
| Coverage | Full circumferential wrap - a continuous barrier | Localised fill - plugs irregular voids and gaps |
| Primary role | Continuous water barrier along the cable; also serves as bedding / insulation | Fills and seals water paths in tight, irregular spaces |
| Swelling | Swells in thickness / height to seal the wrapped layer | Swells to fill the interstice it occupies |
| Conformability | Sheet - wraps around a circular core | Highly conformable to irregular geometry |
| Electrical options | Non-conductive, PET-laminated or semi-conductive | Typically non-conductive or semi-conductive |
| Typical cables | Power cables, optical cable core wrap, armouring bedding | Optical fiber cables (loose tubes, fiber bundles), compact cables |
| Applied with | Tape winding / overlapping machine | Stranding, serving or longitudinal laying line |
When to use which:
Use water blocking tape when you need a continuous wrap around the cable core or between cable layers - the tape is the primary lengthwise water barrier and can also serve as bedding or insulation.
Use water blocking yarn when you need to fill gaps - inside loose tubes, around fiber bundles, or in the interstices between components - where a flat tape cannot fit.
Use both together where a cable needs a core wrap and gap filling; the tape forms the outer barrier and the yarn blocks the internal spaces.
Applications
Optical fiber cables - core wrap and interstice blocking to keep moisture away from the fibers.
Power cables - core wrap and bedding, with semi-conductive grades where the layer sits in the electrical field.
FTTH and access cables - compact, long-life moisture protection.
Submarine and outdoor cables - where water ingress risk is highest and cost of failure is greatest.
Workshop
FAQ
What is the difference between water blocking tape and water blocking yarn? The tape is a flat sheet that wraps the cable core to form a continuous barrier; the yarn is a thin cord that fills gaps and interstices inside the cable. Tape = wrap; yarn = fill. They are frequently used together.
Which tape type should I use? Use non-conductive (ZD) for general core wrapping, PET laminated (ZDF) where extra mechanical strength is needed, and semi-conductive (BZD) for power cables where the tape sits in the electrical field.
How much water can it block? The tape itself is not rated by volume - it is rated by swelling speed and swelling height, given per type in the tables above. The swollen tape seals the layer it wraps.
Does the tape work at high temperature? Yes - after 90 °C for 24 h (long-term) and 230 °C for 20 s (short-term), the swell height remains below the initial value, so the blocking function is retained.
What is the water content requirement? ≤ 9% as supplied.
Can I order a custom width and thickness? Yes - thickness, weight, width and roll length are confirmed per order.
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