Polyester vs Nylon Thread for Motor Winding – Which is Better?
One of the most common questions from motor rewinding workshops, especially from those just starting out, is whether nylon thread can be used instead of polyester thread for motor winding. The short answer is no — polyester is the only correct choice. But understanding why requires looking at the science behind what makes a motor winding thread perform safely over the lifetime of a motor.
The Complete Comparison Table
| Property | Polyester | Nylon | Cotton |
|---|---|---|---|
| Moisture Absorption | 0.4% (negligible) | 2.5-4.0% | 7-8% |
| Heat Resistance | Up to 150°C | Up to 100°C | Up to 80°C |
| Stretch Under Heat | Minimal | Significant (5-15%) | Moderate |
| Electrical Insulation | Excellent | Good (when dry) | Poor |
| Insulation When Wet | Maintains properties | Degrades significantly | Fails completely |
| UV Resistance | Good | Poor (degrades) | Moderate |
| Rot/Mould Resistance | Immune | Resistant | Susceptible |
| Tensile Strength | High | High (but varies with moisture) | Low |
| Cost | Moderate | Lower | Lowest |
| ROHS Certifiable | Yes | Depends | N/A |
| Verdict for Motor Winding | ✓ RECOMMENDED | ✗ NOT recommended | ✗ NEVER use |
Why Polyester Wins for Motor Winding
1. Zero Effective Moisture Absorption
This is the single most important reason. Motors operate in environments ranging from dry workshops to humid coastal cities to submersible underwater conditions. Thread that absorbs water becomes a conductor instead of an insulator. Polyester's 0.4% absorption rate is effectively zero — it maintains its insulation properties regardless of humidity or moisture exposure.
Nylon, by comparison, absorbs 2.5-4.0% of its weight in water. In a humid environment (which describes most of India for 6+ months of the year), nylon thread in a motor winding acts like a wet sponge bridging between copper turns that should be insulated from each other.
2. Dimensional Stability Under Heat
Motors generate heat during operation. A ceiling fan motor reaches 60-80°C, a water pump motor 80-100°C, and industrial motors can exceed 120°C. Nylon thread stretches 5-15% at these temperatures, loosening the winding and allowing turns to shift. This causes vibration, noise, and eventually short circuits between turns.
Polyester maintains its dimensions even at 150°C. The winding stays tight for the entire life of the motor.
3. Electrical Insulation Integrity
The thread's role in motor winding is not just mechanical (holding wire in place) — it also provides supplementary electrical insulation between turns and layers. Polyester maintains its dielectric strength consistently. Nylon's dielectric strength drops significantly when it absorbs moisture, creating potential short-circuit paths.
4. Long-Term Durability
Polyester does not rot, does not degrade from mould, and resists UV exposure. A motor wound with polyester thread and properly varnished can operate for 10-15+ years. Nylon degrades under UV (relevant for outdoor motors) and can lose tensile strength over time in warm, humid conditions.
Industry standard: Every major motor manufacturer in India — from Crompton and Havells to local pump makers — uses polyester thread exclusively. Nylon is not used in any professional motor winding operation.
Why is Nylon Thread Cheaper?
The primary reason some workshops consider nylon is its lower price point. However, using nylon for motor winding is false economy. A motor rewound with nylon thread is likely to fail within 1-3 years (or sooner in humid climates), while the same motor rewound with polyester will last 8-15 years. The cost of a premature rewind (or worse, a motor burnout at a customer's site) far exceeds the small saving on thread material.
What About Cotton Thread?
Cotton was historically used for motor winding before synthetic threads became available. It is still occasionally seen in very old workshops. Cotton should never be used for motor winding because it absorbs 7-8% moisture, rots in humid conditions, has low tensile strength, and provides inadequate electrical insulation by modern standards.
Frequently Asked Questions
Is polyester or nylon better for motor winding?
Polyester is significantly better. It has zero effective moisture absorption, superior heat resistance, does not stretch under temperature, and maintains electrical insulation properties over the motor's lifetime. Nylon is never recommended.
Can cotton thread be used for motor winding?
No. Cotton absorbs moisture heavily, degrades in heat, rots over time, and provides poor electrical insulation. It has been completely replaced by polyester in modern motor winding.
Why does moisture absorption matter in winding thread?
Thread that absorbs moisture becomes a conductor instead of an insulator, increasing the risk of short circuits between winding turns. In submersible motors and humid environments, moisture-absorbing thread can cause complete motor failure within weeks.
Buy 100% Polyester Winding Thread
Parth Enterprises manufactures ROHS and REACH compliant 100% polyester motor winding thread. Guaranteed zero moisture absorption. 25+ years of manufacturing experience.
View Polyester Thread →