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Technical Guidance
How to Choose the Right Cylindrical Battery Insulation Paper for Your Application
In a cylindrical battery module—whether 18650 or 21700—the positive terminal sits dangerously close to the negative casing. The gap is often less than 0.5mm. A single vibration, thermal expansion, or manufacturing defect can cause a short circuit. That is why battery insulation paper is not optional—it is critical.
Battery insulation paper refers to thin, flexible, electrically insulating sheets placed between cells, between cells and nickel strips, and between the battery pack and its enclosure. Unlike general electrical tape, battery-grade insulation papers are engineered for high dielectric strength, temperature resistance, mechanical toughness, and self-extinguishing properties.
This guide covers the most common insulation materials for cylindrical cells—Highland Barley Paper, Fish Paper, Aramid (Nomex®) Paper, and PVC/PET—with practical selection criteria and application tips to help you choose the right material for your specific needs.
Key Material Properties to Evaluate
Before comparing specific materials, it is essential to understand the performance criteria that define a good battery insulation paper. Battery-grade insulation papers are engineered for several key properties:
Dielectric strength – The ability to withstand voltage without breakdown (typically 5–25 kV/mm). This prevents arcing between adjacent cells and conductive components.
Temperature resistance – The ability to maintain insulation properties at elevated temperatures (120–180°C and above), critical during charging, discharging, and fault conditions.
Mechanical toughness – Resistance to puncture from sharp cell edges and nickel strip burrs, ensuring the paper does not tear during assembly or operation.
Thin profile – Thickness typically ranges from 0.08mm to 0.5mm to avoid wasting space in tight pack designs.
Self-extinguishing – Does not sustain flame if ignited by an adjacent cell failure.
Adhesive compatibility – For self-adhesive papers, bond strength and resistance to peeling under vibration and temperature cycles are critical.
Moisture resistance – Low moisture absorption prevents degradation of dielectric properties in humid environments.
Comparison of Common Cylindrical Battery Insulation Materials
| Property | Highland Barley Paper | Fish Paper (Vulcanised Fibre) | Aramid Paper (Nomex®) | PVC / PET Sticker |
|---|---|---|---|---|
| Material | Natural cellulose fiber | Cotton rag paper + zinc chloride | Aramid (aramid) fiber | Polyvinyl chloride / Polyester |
| Dielectric Strength | 15–25 kV/mm | 8–12 kV/mm | 22–32 kV/mm | Medium |
| Temperature Rating | 130–180°C (short-term 220°C) | 130°C (Class B) | Up to 220°C (Class H) | 60–80°C |
| Thickness Range | 0.08–0.3mm | 0.2–3.0mm | 0.05–0.76mm | ~0.1mm |
| Flexibility | Highly flexible | Rigid to semi-rigid | Moderate | Flexible |
| Adhesive Backing | Available (acrylic or silicone) | Not typically | Available on some grades | Available |
| Moisture Resistance | Excellent | Moderate (5–8% absorption) | Excellent | Excellent |
| Best Uses | Wrapping cells, flexible areas, terminal insulation | Rigid insulation, washers, separators | High-performance EV, extreme temperature | Low-cost temporary insulation |
Material-by-Material Selection Guide
1. Highland Barley Paper (The Industry Standard)
Highland Barley Paper (also called Qingke paper) is a thin, flexible cellulose fiber material that has become the industry standard for cylindrical cell insulation. Made from natural renewable fibers and often laminated with adhesive backing, it combines high dielectric strength (15–25 kV/mm) with excellent heat resistance.
Key advantages:
Superior heat resistance – Withstands continuous use at 180°C and short-term exposure up to 220°C, outperforming standard PET or kraft paper (≤120°C).
Strong pre-applied adhesive – High-tack acrylic adhesive bonds firmly to battery casings and resists peeling even under vibration and temperature cycles (-40°C to 180°C).
Thin profile – 0.08mm–0.2mm thickness saves critical space in compact battery packs.
Customizable – Available in any Pantone color for visual differentiation and assembly error reduction.
Eco-friendly – Made from renewable highland barley fiber, halogen-free, and RoHS/REACH compliant.
Best applications: Wrapping individual cylindrical cells (18650, 21700, 26650, 32650), insulating nickel strips, covering exposed BMS board traces, and lining battery enclosures.
2. Fish Paper (Vulcanised Fibre)
Fish paper (vulcanised fibre) is a dense, rigid insulating material made from cotton rag paper treated with zinc chloride solution. Despite the name, it has nothing to do with fish—the name likely derives from “Fischerpappe” (German for fibre board).
Key advantages:
High mechanical toughness – Exceptional puncture resistance (tensile strength 50–80 MPa) makes it ideal for applications where the paper must withstand physical stress.
Rigid structure – Provides structural support in addition to electrical insulation.
Proven reliability – The red insulation rings on every 18650 cell positive terminal are typically fish paper.
Best applications: Cell bottom insulation rings (round washers under the negative terminal), insulating layers between series-connected cell groups, terminal insulation on BMS boards, and pack-to-enclosure insulation sheets.
Recommendation: Use both fish paper and barley paper. Fish paper for structural insulation (washers, rigid separators) and barley paper for wrapping and flexible applications.
3. Aramid Paper (Nomex®)
Aramid paper (such as DuPont™ Nomex®) is a high-performance insulation material made from aramid fibres.
Key advantages:
Superior heat resistance – Maintains stable performance up to 220°C (Class H insulation).
High dielectric strength – 22–32 kV/mm, among the highest of any paper-based insulation.
Excellent mechanical strength – Resists tearing and puncture even in thin formats.
Low moisture absorption – Maintains dielectric properties even in humid environments.
Best applications: High-performance EV battery modules, extreme temperature environments, and applications where the highest level of electrical and thermal protection is required.
4. PVC / PET Stickers (The Low-Cost Alternative)
While PVC is cheaper and commonly available, it offers significantly lower performance.
Limitations:
Low heat resistance – Melts or degrades at 60–80°C, which is insufficient for high-discharge applications or laser welding processes.
Lower dielectric strength – Provides medium-level insulation, insufficient for high-voltage applications.
Poor adhesion over time – May peel under vibration and temperature cycling.
Best applications: Low-cost consumer products, temporary insulation, or applications with minimal thermal and mechanical stress.
Bottom line: While PVC is cheaper, Highland Barley Paper (a specialized cellulose composite) offers superior mechanical properties for EV battery safety.
The Critical Role of Insulation in Laser Welding
One of the most overlooked aspects of cylindrical battery insulation is its interaction with downstream processes—particularly laser welding.
If the insulation paper is misaligned by even 0.2mm, it may cover the welding zone. When the laser beam hits the paper instead of the steel shell, several problems occur:
The paper burns, causing carbonization.
The laser energy is absorbed by the burnt residue instead of welding the metal.
The weld joint fails, compromising the entire battery module.
This is why precision application is as important as material selection. For high-speed production lines, modern insulation paper pasting machines use PLC-controlled stepper motors and servo-driven rotary drums with vacuum suction cups that hold the paper firmly until the exact moment of contact, achieving accuracy locked at ±0.1mm. Machines of this type can complete approximately 4,000 cylindrical finished battery cells per hour.
Common Application Defects and How to Avoid Them
If you are using standalone or manual pasting processes, you may encounter these issues—all of which can be addressed with proper material selection and equipment:
| Defect | Cause | Solution |
|---|---|---|
| “The Flying Sticker” (Low adhesion) | Oil residue on the cell pole or old glue on the paper roll | Use inline plasma cleaning before pasting |
| “The Half-Moon” (Skewed pasting) | Mechanical feed mechanism drift | Use servo-driven rotary drums with vacuum suction cups for ±0.1mm accuracy |
| “The Jam” (Static electricity) | Paper sticking to the blade due to static charge | Use integrated ionizing air knives to remove static charge continuously |
Material Selection Checklist
When choosing cylindrical battery insulation paper for your application, consider the following factors:
| Factor | Questions to Ask |
|---|---|
| Cell format | Are you insulating 18650, 21700, 26650, or 32650 cells? |
| Temperature requirements | What is the maximum operating temperature during discharge and charging? Does the paper need to withstand laser welding heat? |
| Dielectric requirements | What is the voltage of your battery pack? Do you need higher dielectric strength for high-voltage applications? |
| Space constraints | How much clearance is available between cells? Does the paper thickness need to be minimized? |
| Adhesive needs | Do you need pre-applied adhesive, or will the paper be mechanically held in place? |
| Environmental conditions | Will the pack be exposed to moisture, vibration, or extreme temperature cycles? |
| Regulatory compliance | Does the material need to meet RoHS, REACH, UL, or other standards? |
| Production volume | Are you producing prototypes, small batches, or high-volume production? This determines whether pre-cut sheets or roll materials are more suitable. |
| Cost constraints | What is your budget per cell or per pack? |
Summary: Material Selection by Application
| Application | Recommended Material | Rationale |
|---|---|---|
| Consumer electronics (power banks, laptops) | Highland Barley Paper (0.08–0.15mm) | Thin profile saves space; adequate heat resistance; cost-effective |
| EV battery modules | Aramid Paper or Highland Barley Paper (0.2mm+) | High heat resistance; excellent dielectric strength; mechanical durability |
| Power tools / e-bikes | Highland Barley Paper with acrylic adhesive | Withstands vibration and temperature cycles; strong adhesion |
| Energy storage systems (ESS) | Fish Paper + Highland Barley Paper combination | Fish paper for rigid insulation; barley paper for wrapping |
| High-temperature / extreme environments | Aramid Paper or silicone-adhesive Highland Barley Paper | Up to 220°C short-term resistance; stable performance |
| Cost-sensitive / low-power applications | PVC / PET stickers | Low cost; suitable for minimal thermal/mechanical stress |
Conclusion
Choosing the right cylindrical battery insulation paper is not a one-size-fits-all decision. It depends on your specific cell format, operating conditions, thermal and dielectric requirements, production process, and cost constraints.
For most professional battery pack manufacturers, Highland Barley Paper with pre-applied adhesive offers the best balance of performance, cost, and process efficiency—particularly for 18650, 21700, 26650, and 32650 cell applications. For applications requiring structural insulation or washers, Fish Paper remains the industry standard. And for high-performance EV and extreme-temperature applications, Aramid Paper (Nomex®) provides the highest level of protection.
But material selection is only half the equation. Proper application—with precise alignment, consistent adhesion, and integration with downstream processes like laser welding—is equally important. Modern automated pasting machines achieve ±0.1mm accuracy and throughput of 4,000 cells per hour, ensuring that your insulation paper protects, not compromises, your battery pack.