Cars are lasting longer than ever. While that's good for owners, it’s bad for the interior of the vehicle, where stains, cracks and outmoded electronics can undermine the overall driving experience.

So automakers and suppliers are being forced to rethink the way they make everything, from seat fabrics to door coatings to infotainment systems. Everything must be designed for the long haul.

The average age of cars and light trucks on U.S. roads reached an all-time high of 11.8 years in 2018, according to research firm IHS Markit. That’s partly due to improvements in reliability – engines are lasting longer as components become more resilient. It’s also because of lengthier loan terms, which incentivize owners to keep their vehicles longer as they pay off the debt.

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“People are absolutely holding onto their cars longer. Cars are getting better,” said Jake Fisher, director of auto testing for Consumer Reports. “It’s not unreasonable to expect 150,000 miles, trouble-free.”

By 2023, there will be about 84 million vehicles on the road that are at least 16 years old, reflecting a 240% increase from 35 million in 2002, according to IHS.

And that poses a significant challenge.

The last thing automakers want is for their cars to get a reputation for deteriorating quickly on the inside.

Faded plastics or stained fabrics could leave an impression on car owners – and their passengers – that certain brands can't hold up over time, even when their engines are running strong.

And that's just with a limited number of riders.

Imagine the wear and fears on cars used through ride-hailing apps like Uber and Lyft, where passenger volume can be higher and interiors are at risk of wearing out more quickly. And with those customers, there's only one chance to make a good impression or leave a bad one.

“Customers want these soft-touch materials,” said Brent Gruber, senior director of automotive at J.D. Power. “They want things to look really nice, but it also has to be durable and it also has to hold up.”

Leather and armrests

At auto supplier PPG, which makes paints and coatings, engineers are recalibrating their approach to help automakers develop interiors that hold up for 15 years instead of 10. That means paying more attention to coatings used for armrests and seat fabrics, for example.

But boosting the longevity of interior parts by 50% requires an investment in new material composition and design, said Rebecca Liebert, senior vice president of automotive coatings and mobility for PPG.

Coatings and paints are “going to have to be very high quality” to last for 15 to 20 years, she said.

From a practical perspective, that means using more synthetic leather on seats instead of traditional fabrics, which tend to wear out faster, she said. PPG is working on coatings technology to make synthetic leather feel more like the real thing and boost its durability.

“There’s a huge opportunity for automakers to try to find new materials that are not just soft to the touch, but also durable,” Fisher said.

The creation of advanced plastic material that mimics open-grained wood is one example of what to expect, he said. The goal is for automakers to tap into the type of durability associated with the “hard, hard plastics that last forever” on a 1990s Toyota Camry, for example, he said.

“In a way, those are probably the most durable materials you can get,” Fisher said. “They’re somewhat bulletproof.”

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Two of the most commonly cited problems with the interior are material scuffing and seat fabric soiling, according to J.D. Power, which tracks more than 233 specific vehicle problems.

One of the biggest areas for improvement is in what Gruber called “blue-dye transfer,” which is what happens when jeans rub off on lighter seats after heavy usage.

“That’s a really big source of dissatisfaction for consumers,” Gruber said.

The good news is that advancements in interior design have led to a 45% reduction in the “problem rate” for seat scuffing and soiling from 2013 to 2019, according to J.D. Power.

That’s in part due to the shift toward synthetic leather. “Leather is a little more resistant to scuff and soils than cloth materials would be,” Gruber said. “Our research has shown that consumers don’t even know that it’s not leather.”

Infotainment troubles

Another area where automakers are beginning to invest more attention is the durability of their infotainment systems. Infotainment glitches are among the most commonly cited defects in studies of new vehicles by Consumer Reports and J.D. Power.

Since consumer tech improves so rapidly, automakers need to integrate the ability to make over-the-air software updates, which is something that Tesla is credited with pioneering, experts said.

Tesla is able to make wireless improvements to its touchscreens and safety systems, which CEO Elon Musk has trumpeted as a competitive advantage. Traditional automakers have been slow to follow, in part because of the extra expense associated with the connectivity technology required to do so.

But they can’t afford to install infotainment systems in their vehicles that turn out to be dinosaurs within a few years.

“As the average age of personally owned cars gets so much higher, we need to think about the upgradability of those systems,” said Tom Mayor, industrial markets strategy practice leader for KPMG, who consults with auto companies on their future technologies. “How do I make that center console display or that rear-seat entertainment unit just like my phone or my computer or my iPad -- that it gets better over time?”

Many new vehicles now come equipped with the capability of connecting to smartphones using Apple’s CarPlay system or Google’s Android Auto. But the native system installed on the vehicle ages quickly without the ability to be updated.

In a 2018 study, AAA found that Apple CarPlay and Android Auto – which allow drivers to control their phones using the vehicle's infotainment system – are 24% faster than built-in vehicle systems for calls and 31% faster for entering directions.

Mayor said he expects “the majority of my auto clients” to move to “fully connected car fleets” within about four years, which would theoretically allow them to begin making wireless updates to their vehicles.

But that will also require investments in vehicle modems and design tweaks to incorporate the extra storage capacity for computing purposes.

Plus, engineers need to think years down the road, which means incorporating enough processing power “to do more in the future than the day it rolls off the line,” Mayor said.

“That runs counter to a hundred years of how I cost-optimize a car,” he said. But “if I’m going to have a car whose features (improve) over time, then I have to do that.”

Follow USA TODAY reporter Nathan Bomey on Twitter @NathanBomey.