Choosing Insulating Materials for Flexible Heaters

Introduction

When it comes to designing any thermal system, the heating element alone isn’t the whole picture. The performance, safety, and longevity of a flexible heater are then ultimately defined by its insulating materials. These insulating materials are not just a protective covering - they are effectively a part of the construction of a heater and define thermal performance, electrical integrity, and mechanical robustness. For engineers designing embedded systems or any product, selecting the right insulation will be a critical decision that impacts other metrics across your product, such as power consumption and safety.

In this guide, we will take a deep dive into the two most common flexible insulation materials used in modern flexible heaters: Polyimide and Silicone. We will go beyond a superficial description of the materials and examine their primary properties, weigh the engineering trade-offs of one material over the other, and provide a framework for selecting a suitable insulation material based on your specific application.

What are Insulation Materials?

Essentially, an electrical insulation material is a highly resistive material, meaning it strongly resists current flow due to a molecular structure with very few available free electrons to carry a charge. In regard to a flexible heater, this property is valuable to limit current to the resistive heating element; however, the uptake of insulation also holds in the thermal and mechanical applications.

● Dielectric Strength: This metric indicates the ability of an insulator material to withstand a high voltage. Dielectric strength is usually described in Volts per unit of thickness (i.e., V/mil). The higher the dielectric strength, the thinner the layer of material providing the same level of electrical insulation.

● Volume Resistivity: This is the measurement of how much a material resists the flow of current through its bulk. Volume resistivity is also very high for an insulator (approximately 10^16 Ω·cm), resulting in electrical leakage currents being very low.

● Thermal Conductivity (k): This property captures a material's ability to conduct heat through its body. In an insulator, it is important to have low "k", in order to be so that the heat energy generated from the element is not lost out of the heater, and remains aimed towards the target surface.

How Insulation Materials Work

Insulation materials work by limiting the motion of charge carriers (for electrical insulation) or thermal energy (for thermal insulation).

● Electrical insulation: The electrons in an insulating material are bound tightly to their atoms. When a voltage is applied, the insulating material has no free electrons to move and create current flow. This is very different from using a conductor like copper because, in the case of copper, the electrons can move freely throughout the material.

● Thermal insulation: Heat is more or less simply transferred through a solid material through the atomic lattice's vibrations (phonons). In a good thermal insulator, the structure of the material effectively scatters vibration energy, which limits the ability of heat to traverse the material.

Cross-section diagram of a flexible heater showing the insulation layers directing heat.

Why Insulation Materials are Critical for Flexible Heaters

A flexible heater's insulation layers perform three simultaneous and critical functions:

1. Electrical Safety and Reliability: Insulation's primary function is to electrically isolate the resistive heating element from the device chassis and user. The insulation material possesses high dielectric strength, as well as high resistivity to avoid short circuits and current leakage, ensuring the end user is not exposed to electric shock.

2. Thermal Efficiency: The insulation acts as a thermal barrier, directing heat to flow. Insulation is placed above and below the heating element, so when the heating element is energized, heat is forced to conduct through the insulation to the mounting surface.

3. Mechanical Durability: The thin foil metallic heating element is very fragile. The insulation encapsulates and protects the heating element from mechanical stress, vibration, flexing, moisture exposure, and/or chemical exposure.

Types of Insulation Materials for Flexible Heaters

While there are many options for insulation materials, Polyimide and Silicone are the two most utilized in the flexible heater market as they strike a good balance for their properties.

Polyimide as an Insulation Material

Polyimide is an advanced polymer, the most recognized version before its time under DuPont's trade name, Kapton®. It is the preferred insulation material for high-tolerance, high-precision, and high-performance flexible heater applications.

● Key Characteristics: The polyimide film is well known for its thermal stability over a very wide temperature range for a flexible heater material, typically from -200°C to 260°C. Polyimide possesses very good dielectric strength, allowing its use in very thin layers and overall electrical insulation.

● Advantages & Applications:

○ Ultra-Thin Profile: Allows for flexible heaters that in ultra-thin and lightweight, ideal for applications of limited space.

○ High Power Density: The advantage of exposing polyimide to high temperatures as a medium allows for a design with uniform higher power output per unit area.

○ Fast Thermal Response: The low thermal mass of a thin polyimide heater, like those available for custom order through JLCPCB Flexible Heater, allows for rapid heating and cooling cycles.

○ Applications: Aerospace, medical diagnostic equipment, and analytical instruments where precision and performance are critical.

Silicone as an Insulation Material

Silicone insulation is a highly versatile and durable elastomer used in a wide array of flexible heater applications, particularly where ruggedness and moisture resistance are key.

● Key Characteristics: Silicone rubber has an excellent degree of flexibility, as well as accommodates a sizable amount of compressibility and extension. Further, this elastomer has a wide degree of operating temperature, -60 °C to 230 °C is typical, even when subordinate to outstanding resistance to moisture, weathering, and various chemicals.

● Advantages & Applications:

○ Superior Flexibility and Durability: Heaters built with this material, such as the custom silicone heaters from JLCPCB Flexible Heater, are perfectly suitable for conformance to even highly irregular surfaces. They are robust and can withstand mechanical shock and vibration remarkably well.

○ Excellent Moisture Resistance: Silicone is, by its very nature, waterproof and is probably the only elastomer suitable for applications exposed to moisture, condensation, or wash down cycles.  

○ Cost-Effectiveness: In general, silicone is a more affordable elastomer as compared to polyimide.

○ Applications: Industrial Equipping (i.e., drum heating), food service equipment, battery warming in electric vehicles, and outdoor enclosures.

Polyimide VS Silicone: What are the Differences?

The choice between Polyimide and Silicone ultimately depends on the specific requirements of your application.

Polyimide vs. Silicone - A Comparative Analysis

Which Is Right for Your Design?

Selecting the proper material for your project is one of the most pivotal engineering decisions you will make. This is where a service like JLCPCB Flexible Heater excels because it helps connect the dots between material theory and a finished working part. Standard heaters commonly do not fit unique applications, but with a fully customizable service, an engineer can get a heater that exactly fits their particular desired dimension, shape, and power density.

To engineers involved with R&D or prototyping, the No MOQ is a significant advantage in quickly iterating through different designs (without the burden of committing to mass production), as it means that the project will not be held up waiting for parts to arrive for its erection (construction). Getting an instant quote online for fast lead times also helps with project planning/budgeting. The platform is designed for engineers to upload standard design files (such as Gerber or CAD drawings).

JLCPCB Flexible Heater is a one-stop thermal integration service with an option for expert consulting to help expedite validating their prototype (if needed). It offers free design support, assisting customers in selecting or designing flexible heaters that precisely meet their specific requirements. This ensures the delivery of optimal thermal solutions customized for each application.

Conclusion:

Choosing between Polyimide and Silicone is a classic engineering trade-off. Polyimide heaters provide exceptional performance for precision, high-temperature, and space-constrained applications. Silicone heaters serve as a durable, flexible, and economical choice for industrial and moisture-sensitive applications.

In the end, you want the best insulating material for your design, electrical, thermal, and mechanical requirements. When you are familiar with these key materials and with a modern manufacturing platform like JLCPCB Flexible Heater, engineers are prepared to exceed commodity components and develop custom thermal solutions designed specifically for their needs, accelerating innovation and market reliability.

Frequently Asked Questions (FAQs)

Q: What is the actual heating element made of in these flexible heaters?

A: The heating element is typically a thin, flexible foil made from a resistive alloy like Nichrome (Nickel-Chromium) or Constantan (Copper-Nickel).

Q: Can temperature sensors be integrated into these flexible heaters?

A:  Yes, it is common to integrate sensors like thermocouples, RTDs, or thermistors directly into the heater assembly.

Q: How are flexible heaters typically mounted?

A: The most common mounting method is using a pressure-sensitive adhesive (PSA) backing.

Q: Does the color of the polyimide or silicone affect performance?

A: Generally, no. The color is inherent to the material's composition and does not significantly impact performance.