Polyimide Flex Heater vs Silicone Rubber Flex Heater Limitations
Hi-Heat Industries
Flexible heaters are used in products across many industries, from medical to food service. Manufacturers need heaters that work with their existing product design. A flexible heater can meet those requirements if a piece of equipment has a narrow, curved surface and needs temperature regulation.
Two of the most popular types of flexible heaters are polyimide and silicone rubber. Both can handle extreme temperature fluctuations and exposure to certain liquids. The thin but durable design makes both ideal for various situations. However, both polyimide and silicone rubber flex heaters have their limitations. It’s essential to look at their advantages and disadvantages as you shop for the right solution.
What are flex heaters?
Flexible heaters supply heat to a variety of surfaces. A flex heater may regulate temperature, reduce condensation, or provide heat to those using the equipment.
Different uses call for different sizes and functionality. For that reason, flex heaters come in many designs and build, each with its benefits. Two of the most popular flex heaters are polyimide and silicone rubber. You can buy both options in many quantities and varying sizes.
Polyimide flex heaters
Also known as Kapton heaters, polyimide heaters consist of Kapton film. DuPont, a top producer of scientific products worldwide, developed this film. DuPont Kapton films have been used for over 45 years and have become the industry quality standard. They’re sourced for space missions, solar panels, and much more.
With a polyimide heater, you get a thin film that’s built to conduct heat. The thin build also makes it easy to shape and cut to exactly the fit you need. For that reason, polyimide is often sought for those difficult-to-fit applications.
Silicone rubber flex heaters
Silicone rubber flex heaters are durable. If you’re concerned about damage from chemical exposure, these heaters are best for you. They feature a wire-wound or etched-foil heating element with a rough or smooth silicone rubber texture.
The construction of silicone rubber flex heaters can vary from manufacturer to manufacturer. Hi-Heat offers both wire-wound and etched-foil silicone rubber heaters with the following designs.
- Etched foil: Custom software calculates the heating element to determine voltage, wattage, and resistance. Nickel alloy foil is acid-etched into the element with the foil, then vulcanized to the rubber.
- Wire wound: Hi-Heat combines fiberglass twine with an acceptable nickel-chromium alloy core to create the heating element. The equipment used for winding is electronically controlled to ensure precision. Hand-wound circuits further ensure peak performance. A second layer of silicone rubber protects the finished heating element.
Benefits of polyimide flex heaters
Regarding tear resistance, finding a flex heater that beats Kapton polyimide heaters is hard. Kapton film has an ultimate tensile strength of 231 to 234 MPa or pounds per square inch. DuPont stress tests its Kapton film to ensure it can withstand various stresses. There are a few benefits of using polyimide flex heaters for your applications.
Larger temperature threshold
Temperature tolerance is essential for any flexible heater. Polyimide film has a range of -319°F to 392°F. So, it’s a great option for products exposed to extreme temperatures. Where other types of organic polymer-based materials would struggle, polyimide holds up. Polymide can handle environmental temperature extremes and heat outputs from the enclosed element and surrounding equipment. The film’s properties don’t change under these extremes, providing the same protection you’d have at 70°F.
Chemical resistance
Since flex heaters are used in various equipment, the industry looks for materials that can withstand many factors. One thing that comes up often is chemical exposure. Polyimide film can withstand most chemicals and solvents, so spills and leaks won’t be a problem. This resistance also means it can hold up against corrosion over time.
Tear resistance
Flexible heaters often have to fit into tight, curved spaces. The tricky installation process can lead to damage to less durable components. The high tensile strength of polyimide film makes it ideal for these conditions. On a production line, this can save time as workers don’t have to take extreme care while installing.
Uniform thermal distribution
Polyimide can handle temperatures ranging from -319°F to 392°F, and the composition provides even heat distribution across entire surfaces. This means you can rely on the heater to do the job, even when covering a large area. This thermal distribution applies even in conditions where equipment rapidly heats and cools.
Thin, flexible build
Polyimide’s thin profile makes it versatile enough to squeeze into various spaces. Generally, polyimide flex heaters are only 0.18 mm, with a bend radius of at least 0.8mm. This gives it the flexibility that other materials can’t provide.
Minimal outgassing
Outgassing can be a problem for components, particularly those in a closed environment. The gases can become trapped inside equipment, impact sensors, and other parts. Polyimide flex heaters have low outgassing properties, so this won’t be a concern.
Benefits of silicone rubber flex heaters
Silicone rubber is a popular material, so it’s no surprise that it’s often chosen for flex heaters. Like polyimide, silicone rubber flex heaters are more durable than other materials. Here are a few benefits of silicone rubber flex heaters.
Resistance to moisture
Temperature fluctuations can damage electronics, mainly if moisture builds up. Silicone rubber resists moisture, whether from condensation or direct contact with liquids. It can even hold up under exposure to alcohol, sodium hydroxide, and grease.
Easy to attach
When looking for flex heaters, manufacturers must look at the installation process. If the heater needs to attach to other parts, it’s important to consider how to connect them. Silicone rubber heaters can be laminated or attached to connectors to quicken installation.
Larger temperature threshold
Like polyimide film, silicone rubber can withstand extreme temperatures. Hi-Heat’s silicone rubber flex heater can handle a continuous operating temperature of up to 392°F and intermittent temperatures of up to 600°F. They also maintain stability in temperatures as low as -70°F.
Superior temperature control
Temperature management can be tricky with flex heaters. Silicone rubber heaters can handle complex heat distribution, making them ideal for challenging applications. You can also attach temperature sensors to monitor the heat output.
Range of options
There are two silicone rubber flex heaters, which means more customizability. You can choose from wire wound or etched foil, a heating element encased in silicone rubber.
- Wire wound: Offers distributed wattage at a lower energy output per square inch. Wire-wound rubber heaters are best for those who need more complex heat distribution.
- Etched foil: Offers quicker production at a lower cost than wire wound. You can get lower pricing on smaller quantities if you only purchase a few heaters.
Rapid heat transfer
Silicone rubber can transfer heat rapidly from one surface to another. That means you’ll get rapid heat-up even when you’re using a silicone rubber heater on a larger surface area. Silicone rubber is often a great choice if you need a heater that can reach a fixed temperature quickly.
Limitations of polyimide flex heaters
Unfortunately, flex heaters have some limitations, no matter which build you choose. For polyimide flex heaters, the limitations relate more to installation and use than the material itself.
Leaks are possible
While polyimide heaters can protect components from moisture and extreme temperatures, they’ll only work if they’re set up correct. If there isn’t a tight seal, air and moisture can get around it and affect other parts. The heater must have the required tensile strength to keep it from shrinking and expanding with temperature changes.
Degrades with age
As durable and resilient as polyimide is, it degrades with age. You might not get the same protection after a few years as when it was new. The heater will degrade faster if exposed to the maximum operating temperature of 400°F regularly. This increases the risk that it won’t perform as well over the years.
Customizability affects performance
One benefit of polyimide flex heaters is that they offer even heat distribution. But, if you change the heater’s shape to fit a product, it may not offer the same distribution. This is especially true if there are cutouts to accommodate attachments. You might find a lower heat output in those areas, affecting efficiency.
High cost of prototyping
Polyimide film is an expensive material, which makes prototyping tough. You’ll likely want to see what the heater will look like and test it before ordering it in bulk. However, the cost of the film can make prototyping more expensive than with other types of flex heaters.
Limitations of silicone rubber flex heaters
As durable as silicone rubber is, it does have some limitations. Here are a few limitations to consider.
Limited chemical resistance
Silicone rubber flex heaters can resist many chemicals, but not all. They don’t have the same chemical resistance as polyimide heaters. Avoid using them in environments with exposure to petroleum or sulfuric acid.
Reduced temperature range
Silicone rubber can withstand temperatures from -70°F to 392°F. Though impressive, it isn’t as durable as polyimide film. If you need to reach temperatures up to 600°F on occasion, silicone rubber could work. Otherwise, you’ll want to stick with Kapton heaters.
Designed for large coverage
Silicone rubber flex heaters provide heat to large surface areas. For smaller spaces, you’ll find polyimide heaters that fit your needs. Silicone heaters also aren’t great for curved spaces. Instead, they work best when you need a flat heater.
Easily damaged during installation.
Keep in mind that silicone rubber flex heaters can be damaged. They are durable, but you must avoid pulling or over-flexing them to preserve their original shape.
Not moisture-proof
Moisture and liquid exposure aren’t immediately deadly to a silicone rubber heater. But that doesn’t mean they can be immersed in liquid. Avoid spraying or immersing a silicone heater in water before or after installation.
Maintaining proper equipment temperatures is essential to protect sensitive internal components. Both polyimide and silicone rubber flex heaters protect against moisture and temperature. As durable and resilient as both are, though, they have their limitations. So, it’s essential to know exactly how you’ll use each part before adding them to your manufacturing. Our flexible heater experts can work with you to develop a solution that will suit your business needs. Contact us today to find out how we can help you.
