Here’s What The Inside Of A Heated Seat Looks Like, And How It Works

Recently while browsing a BMW i3 forum, I spotted the image you see above taken with an infrared thermal-imaging camera. It shows the pattern of the heating elements within a heated seat, so I figured I’d show you all what these things look like inside, and how it all works.

The photographer, Kurt Edelbach, shot these pictures of his BMW i3’s driver’s seat and posted them to a BMW i3 page on Facebook.

“Seat heating pattern, taken ~20 seconds after turning on Lev 3. Lev 1 is hot enough for me,” he wrote. “Top looks like moose antlers – Designed by a Swedish engineer with a sense of humor?” Huh; I guess those do look like antlers:

So, what exactly are we looking at, here? Well, a heated seat works in a fairly simple fashion. Anytime you send a current through a material, you get what are called “I^2R” losses. Basically, this is the internal resistance of the material (a wire or “cable” in this case) turning power into heat. If you’ve used an electric stove or a space heater or really anything else that uses a “heating element,” then you probably get the idea.

A heated seat pad is basically just some wires, carefully spaced in a felt pad that taped atop the seat cushion (just like you see above), that turn current — which you control with a switch on your HVAC panel — into warmth for your butt and back to enjoy.

The patterns of these heating patters are fun to look at:

The cables are made of all sorts of materials. Seat supplier Bekaert offers three different cables:

• Bekinox® VN: Made from ultra-fine stainless steel microfilaments, these are the most durable on the market
•  Bekiflex®: Steel core with an outer layer of nickel, zinc or copper
•   Bekiflex® Hx: Helix cables with a hybrid structure combining a textile core and conductive wires – new –

So basically you’ve got stainless steel; steel with nickel, zinc, or copper; or a blend of a fabric and some kind of conductor.

Of course, there’s more to a heated seat than just some wires embedded in a felt pad. There’s also a controller and a Negative Temperature Coefficient (NTC) thermistor (a thermistor is a device whose resistance changes as a function of temperature; the controller can detect this change in resistance to determine the seat’s temperature). The sensor company “Amphenol” has a nice PDF that describes how it all works; you can check it out here. Here’s a quote from Amphenol:

The temperature of a heated seat is measured by a NTC thermistor that is embedded between the foam pads of the seat. The thermistor monitors the seat’s temperature and feeds this information back to the controller that regulates the seat’s temperature.

The video below gives a very general ideal of the feedback loop:

In the research for this article, I happened upon some gold. For example, it turns out Hyundai asked the U.S. Government for EPA credits for its heated seat tech, with the idea being that one can save quite a bit of fuel with a more efficient heated seat system:

So actually, what Hyundai is asking for is carbon credits for a more complex seat heating/cooling system that utilizes airflow and a Thermoelectric Device, or TED, to more efficiently heat/cool the passenger. A thermoelectric device is something I used when I helped develop the hybrid battery pack on the Jeep Wrangler JL mild hybrid; it basically uses a current to create a temperature difference between two sides of a cooling plate:

Solid state heating and cooling company Promethient explains it on the web page of its brand “Thermavelence“:

Thermoelectric Devices and the Peltier Effect

Solid state heat pumping is accomplished with a specialized semiconductor called a thermoelectric device, or “TED.” TED’s use the flow of electrons to create the Peltier Effect within the semiconductor. The Peltier Effect is created at the junction of P and N type semiconductor elements that are laminated between two ceramic plates. With the application of a voltage and the flow of current, one plate will heat and the opposing plate will cool. When the polarity of the applied voltage is reversed, the heat flow will reverse.

Here’s a YouTube video describing this type of seat heating/cooling, if you’re curious:

I found a lot more while researching for this article. For example, here’s a whole document about seat heater injuries:

Seat Heater Injuries: An Overview Seat heaters have been installed in automobiles since the 1970s. Today they are commonplace – in about 30 percent of all vehicles in the 2010 U.S. fleet. Despite their increasing ubiquity, seat heaters are not designed to any voluntary or mandatory industry standards, leading some manufacturers to set the maximum temperatures of their seat heaters in excess of human heat tolerances. Others fail to include automatic timed shutoff switches. While most occupants are able to discern when the seat heater has exceeded human limits, occupants who suffer lower body sensory deficits caused by paralysis, diabetes and neuropathy are at risk. These design flaws have resulted in severe burns to disabled vehicle occupants—a problem that has been validated by consumer complaints, the medical literature and demonstrated in testing.

If you’re extremely intrigued by heated seats and want to learn about their importance in the auto industry at large, market research and management consulting firm Lucintel has quite a deep dive here. Here’s a quote:

The global automotive seat heater market is expected to reach an estimated $1.7 billion by 2030 with a CAGR of 3.6% from 2024 to 2030. The major drivers for this market are increasing vehicle production and growing demand for comfort and safety features.
The automotive seat heater market primarily uses raw materials such as heating wires made from nickel-chromium alloys, silicone or polymer-based heating pads, and various types of textiles or leather for the seat covers. Pricing varies based on the complexity of the heating elements and integration with electronic controls; basic seat heaters are relatively affordable, while advanced systems with additional features like adjustable temperature settings and quicker heating times are more expensive. Overall costs are influenced by material quality, technology, and production volume.
• Lucintel forecasts that carbon fiber meshed weave heating pads will remain larger segment over the forecast period due to its excellent strength and low-voltage heat generation capability.
• Within this market, passenger car will remain the largest segment.

Hot damn! Carbon fiber mesh weave! This, Lucintel mentions, offers a potential efficiency advantage of a traditional metal cable-style heated seat setup. Here’s what carbon fiber heating elements look like:

Wow I went down a rabbit hole. All I wanted to do was share those colorful pictures from that thermal imaging camera!