When Nike honcho Phil Knight commissions his swoosh-stripe Mount Rushmore somewhere in the wilds of the Pacific Northwest, the Air Max 95 will be one of the shoes that will be carved into the Precambrian granite outcropping. The Air Max 95 isn't the best Nike runner ever made, it's arguably (sorry Air Jordan junkies) the best Nike shoe ever made, an object burrowed deeply into the popular culture. Collectors flocked to it, kickstarting what would become a $75 billion global industry fueled by hype beasts, sneakerheads, and enough aspirational consumers to fill the Mariana Trench several times over. Since it's 1995 debut, the Air Max 95 has remained a perennial bestseller. Nike churns out several new versions every year. The number of colorways is staggering: over 150 and counting. Such ubiquity has done nothing to diminish the shoe's cachet. It continues to be been worn by artists, actors, pop stars, criminals and, yes, even actual athletes.

Nagomo Oji knew he was stepping into history when he laced up a pair of Air Max 95s last month in Saitama City, Japan, a commuter sprawl 10 miles north of central Tokyo. What made Oji's shoes so special was their pedigree. Anybody can walk into Foot Locker and buy a pair of Air Maxes for 160 bucks. Oji's shoes were something quite different. To use the sneakerhead vernacular, they were "DS" (dead stock), a discontinued model that's new, unworn, and unboxed. Even better, they were "OG. Not "original gangster," just "original." In other words, these vintage kicks were highly collectable, a pristine example of the very first Air Maxes that dropped two decades ago.

But something insidious has been happening to those shoes, and every other pair like them, over the years. They've been crumbling away to nothing as they sit tucked in boxes or hidden in closets. The materials used to make them degrade over time, causing the shoes to fall apart, rendering them worthless.

As soon as he planted his feet, Oji sensed something was terribly wrong.

Untouched specimens like Oji's are as rare as Siamese hermaphrodites and can fetch over $2,000. But Oji had no interest in selling his Air Max 95s. For him, the shoebox was a time capsule that conjured fleeting images of lost youth and harkened to a forgotten period when collecting kicks was a hobby, not an investment. Besides, how could you put a price on old-school details like midsole "BWs" (big windows) that contained the encapsulated nitrogen bubbles, or the PSI specs stamped on the sole from toe to heel ("20, 25, 5,"), like an Enigma code?

A pair of 2010 Nike Air Max 95 Retros, copied after the original 1995 design. Molly Cranna/WIRED

Much had happened since Oji purchased these Nike runners. He no longer defined himself by the shoes he wore. Vanity had been undermined by adulthood and responsibilities. He was a grown man now, a father of 2-year-old twins. As he appraised his newly shod feet, a smile creased his lips. It might not be possible to relive the past, he thought. But this was the closest thing to it.

As soon as he planted his feet, Oji sensed something was terribly wrong. The midsoles flattened, and his footing became strangely unstable. He didn't realize it at the time, but the polyurethane (PU), that squishy, shock-absorbing material sandwiched between the upper and the outer sole, was more than ten years past its projected lifespan.

After just one step, the hardened PU foam fractured and collapsed, like arid soil crumbling beneath the boots of a Dust Bowl Okie. Oji looked down in disbelief. With the inner soles completely detached from the uppers, his feet were actually touching the ground. His beloved Air Maxes had just morphed into Fred Flintstone shoes.

This was absurdly counterintuitive. Scientists and conservationists have warned that plastics would languish in landfills for 500 years. And yet Oji's polyurethane midsoles had been reduced to a sticky trail of biodegraded fragments.

In the wake of this disaster, Oji did what any other grieving Millennial would do: He snapped some photos of this "Cool Grey/Neon" mess and uploaded them to Twitter. "Sad news," he tweeted. "After wearing AIR MAX 95s for the first time in 20 years, they broke apart after one step, before I could get out the front door."

The feedback ranged from empathy (Oh, that was such a popular model.) to sarcasm (Congratulations!) to clinical assessment (That model, if brand new with box, is 200,000 yen). All Oji could muster in response was, "Battered and collapsed."

It's unclear if he was referring to the shoes or himself. He concluded the tweet by adding the only thing someone could say after watching the last vestige of youth destroyed: "I feel sick." It wasn't a total loss. Oji raised his social media profile dramatically. Those grisly postmortem shots have been retweeted over 12,000 times.

Trouble Underfoot

It's not just Nikes that fall victim to crumbling shoe syndrome. New Balance, Reeboks, Asics, and every other trainer with PU construction eventually will fall apart. Consider this video tour of an Adidas store in Buenos Aires, owned by a geriatric hoarder who can't bear to part with his precious inventory. The musty showroom has no customers, but is crammed floor-to-ceiling with row upon row of tri-stripe 1970s gems. It's the Adidas mother lode: hundreds of pairs of DS/OGs ranging from track and field models to soccer cleats.

Jordan Michael Geller holds a pair of Nike Air Max 97s. Molly Cranna/WIRED

All of these shoes were found in various states of decay in one of the biggest known cases of PU mass destruction. Seven minutes into the video, collector Robert Brooks pulls a forgotten artifact labeled Silver Wind from the stacks. He's elated. It's an obscure Adidas runner that's eluded him for "a long, long time." But as he lifts the shoe, the sole peels off and falls into the box. Recounting the story later, he sighs and whimpers "No!" stretching out the syllable for a few seconds, like a Loony Tunes character plunging from a high cliff into the abyss.

No one is more familiar with crumbling shoe syndrome than Jordan Michael Geller. The University of San Diego law school alumnus achieved C-list celebrity in 2012, when Guinness officially certified him as the owner of the world's "Largest Collection Of Sneakers/Trainers." For several months, that massive stockpile—2,388 pairs of shrink-wrapped Nikes, which eventually top 2,500—was on display in Geller's ShoeZeum, a rambling, 7,500-square-foot pop-up exhibit in downtown Las Vegas.

It became such a sneaker shrine that Nike CEO Mark Parker made a pilgrimage to see some of the eBay listings Geller had outbid Nike on, including a pair of Japanese-made 1972 Marathons1. Although he worships the swoosh stripe, Geller can't resist tweaking his favorite shoe brand. "Whoever Nike hired to bid on their stuff is a total amateur. It's really comical. Their strategy is so bad that a 5-year-old could swoop in and outbid them."

If your Nikes are ten years old or older, wear them at your own risk.

Or a 37-year-old lawyer with a shoe fetish. Geller says he beat Nike on those blue nylon Marathons with a winning bid of $1,300. He also says Nike's eBay User ID is Papaman. A good thing to know when you're jockeying for those priceless 1960s runners hand-sewn by Oregon track coach and Nike co-founder Bill Bowerman.

Geller recently sold a large chunk of his Nike archive on eBay: 2,000 pairs (give or take). The remaining 500 pairs are the most valuable, including a $100,000 eBay lot that he calls "the holy grail of Nike skateboarding."

1972 Nike Marathons. Molly Cranna/WIRED

He addressed the decision to sell his collection last year in the YouTube video "Three Reasons Why I'm Selling My Shoes." Two reasons had to do with PU's limited shelf life. As Geller explains in the video, he was abdicating his Nike throne because he couldn't bear to watch his magnificent dead stock slowly degrade. For one thing, the synthetic parts of the shoes, particularly the soles, were turning a hideous shade of yellow. Worse, some shoes were actually falling apart. Reason No. 3, Nike's decision to "retro" (rerelease) certain classic models. That was the final indignity. He had sat on these blue chips long enough, and now he was dumping them.

As much as some hardcore sneakerheads loath the "retro" trend, Geller stresses that the PU problem trumped all other considerations. "If your Nikes are ten years old or older, wear them at your own risk," he says. The public service announcement continues as he launches into a litany of escalating symptoms that every collector is familiar with: "The air bubbles in the midsole deflate and become flat as a pancake. The glue gets crusty and becomes visible. Then the poly and all the white parts, the netting and mesh, turn yellow. Yellowing is a big problem. Finally, when the soles separate from the uppers, that's it. Say goodbye to your expensive shoes."

Despite such cautionary tales, inflated prices continue to be paid for DS OGs that will inevitably decay with the passage of time. "Yeah, they're OK with it," Geller says of his fellow collectors. "That may seem irrational and borderline insane to most people, but that's what this hobby is all about: irrational behavior and lots of insanity." Any advice for all the hype beasts out there? Geller doesn't hesitate: "Three words: Shoes fall apart."

The Chemistry of Decay

The Nike king is constantly reminded of just how tenuous and fragile the molecular PU bonds are in the early models. "Last week, I broke out a pair of 2006 Jordans," he says casually, as if wearing a 9-year-old pair of DS Jordans was barely worth mentioning. "Almost instantly, the paint started chipping and cracking. It was like an earthquake hit the midsoles." His disgust is palpable. "After ten minutes, they looked like shit."

A pair of low top Nike Skateboarding Dunks. Molly Cranna/WIRED

According to "Studies On Ageing Performance Of Some Novel Polyurethanes," a paper published in the Journal of Chemical and Pharmaceutical Research (PDF, S. Gopalakrishnan/T. Linda Fernando, 2011), that midsole "earthquake" Geller survived is known among polymer scientists as "ESC"—environmental stress cracking.

This passage says it all: "Poly (ester) urethanes and poly (ether) urethanes, which are widely used for long-term applications, have been shown to degrade under hydrolytic conditions and in oxidative environment respectively. In addition, ESC of polyurethanes is also another important way of polyurethane degradation. Degradation can lead to significant changes in the polymer mechanical properties, surface chemistry, and structure, leading to malfunction."

That's right, the two things that make human life possible—water and air—are killing our shoes. Their role in degrading polyurethane can be attributed to the chemical processes of hydrolysis (in the presence of moisture) and oxidation (in the presence of oxygen). Simply put, the humidity in the air, and, yes, even the air itself, seeps into the PU and, slowly but surely, breaks it into itty-bitty sticky pieces. Delve deeper into the subject, and the news only gets worse. Bottom line: Pricy collectables shouldn't be made out of PU.

The two things that make human life possible–water and air–are killing our shoes.

"Both mechanisms—hydrolysis and oxidation—are accelerated in foam polyurethane," says Northwestern chemistry professor SonBinh T. Nguyen. "Both of these mechanisms are also accelerated at higher temperatures, and oxidation is further accelerated by light. Mold growth is another degradation mechanism. This is a fairly common phenomenon."

Common, sure, but for many, many people, totally shocking. And this footwear blight isn't limited to athletic shoes. Wolverine, L.L. Bean, Vasque, Clarks, Rockports, Ecco… Enough PU wardrobe malfunctions occur across the globe to keep the Customer Service lines in Mumbai humming 24/7.

The typical PU "malfunction" scenario goes like this: Clueless employee leaves a trail of black goo throughout the office, but nobody notices because office floors are always filthy. The employee returns home and mucks up his own floors. This black goo, however, doesn't go unnoticed. Clueless employee curses, tosses shoes in trash, assumes he stepped in something, and thereafter is vigilant about not walking into puddles of corrosive acids on the way to work.

Original Air Max 97s showing polyurethane degradation and sole separation. Molly Cranna/WIRED

Even some people who work in the PU industry are clueless. "This is quite surprising," says Robert Luedeka, executive director of the Polyurethane Foam Association, a trade organization charged with promoting the use of flexible PU foam. "I've never seen a technical paper on polyurethane shoes falling apart. But now that you mention it, I've owned several pairs of shoes that started cracking inside and outside. I didn't know if they were just poorly made or if I stepped into something."

Water in the air, oxygen in the air, mold spores and gaseous pollution in the air, light, high temperatures, not to mention temperature fluctuations—it turns out Earth is an extremely hostile environment for foam PU. No wonder all those Adidas in Buenos Aires decomposed like corpses.

Knowing when a shoe was manufactured and how it was stored is only part of the equation that determines its longevity. The big unknown for collectors is the proprietary chemical formulations used in the manufacturing process. It turns out that adding polyester to the secret sauce (not unusual) speeds up the "degradation mechanism."

Tim Ray Blake, a Stanford chemist who studies biodegradable polymers, says this is why some shoes fall apart faster than others. "Different polymer formulations can be used to tailor the physical properties of different types of shoes," says Blake. "Some of these formulations incorporate polyester segments, resulting in polyurethane-polyester copolymers. Since ester units are more susceptible to hydrolysis than urethanes, these materials degrade faster than pure PUs or PUs of different compositions."

Point taken. Which is one reason why the 1985 Air Jordan 1 "Breds" (black/red colorway) are coveted by sneakerheads; the midsoles are made of rubber instead of polyurethane.

First synthesized by the German chemical giant IG Farben in 1938, PU found its way into all sorts of industrial applications by the mid-20th century. The versatile thermoplastic polymer was everywhere. The anti-corrosive coatings on Navy war ships were made with PU. Beer barrels were insulated with the stuff, too. Beauty queens wore bathing suits woven with PU-based Spandex, and NASA lined Mercury space suits with it. By 1953, the "synthetic leather" sole on Converse All Star basketball shoes were PU.

Polyurethane construction in shoes has ramped up over the past several decades. Light, flexible, comfortable, durable, inexpensive; in many ways, it's the ideal sneaker material. From the crude waffle runners or the early 1970s to the latest CAD-designed Lebron 12s and Kobe 10s, tricked out with Kevlar and carbon fiber, PU-injected foam continues to be a miracle material for shoe manufacturers, and a ticking time bomb for sneakerheads.

"Nike and Adidas knew back in the early '90s that their shoes had limited shelf life," says Alfons Tremml, the commercial manager for Huntsman, a German polyurethane supplier. "When they outsourced their manufacturing to Indonesia and Vietnam, they noticed that high heat and humidity accelerated PU degradation."

Polyurethane degradation seen on a pair of Air Max 97s. Molly Cranna/WIRED

The question that every serious collector wants to know is this: Can the dreaded sneaker plague be eradicated, is it possible to prevent hydrolysis, oxidation, and everything else in the atmosphere from laying waste to all of this ridiculously expensive footwear? How about building an underground walk-in closet that maintains strict, climate-controlled, museum conditions: 68-72 degrees Fahrenheit/45-55 percent relative humidity? And just to be safe, throw in a truckload of silica gel packs to counteract that nasty hydrolysis thing.

"I would say that 45 percent humidity is still quite high over the course of five to ten years," says Stanford chemist Tim Ray Blake, pessimistically. "That's a lot of moisture."

Professor Nguyen agrees. He chuckles when told that collectors scatter silica gel packs around their heirloom shoes like confetti. "That would have a minimal effect," he says. Being a man of science, though, he believes even the most vexing problems can be solved. He pauses to consider possible solutions. After careful analysis—placing the shoes in a vacuum is suggested, but quickly dismissed; if there's plasticizer in the PU, it may seep out and cause degradation—he concludes that the only solution is to place the shoes in an airtight steel vessel filled with argon. Yeah, science!

"The PU would not degrade because argon has an extremely low chemical reactivity," explains professor Nguyen. This is an old trick scientists use when they want to prevent an important lab sample (or their tuna sandwiches) from being degraded by undesirable chemical reactions, which frequently happen to be oxidation and hydrolysis.

It's only a matter of time before some guy in Brooklyn starts churning out "artisanal" argon chambers constructed from cold rolled 18-gauge steel, and selling them to sneakerheads for an ungodly price.

Restoring History

For everyone else, there's a thriving cottage industry of self-taught PU cobblers that specialize in what's known in the sneaker trade as "sole swaps." If, for instance, your 2001 Air Jordan Black Cement 3s fall into disrepair, send them to Justin Douglas in Fort Worth, Texas. Don't forget to include the "donor" midsoles. A used pair of retro 2011 Black Cement 3s ($50-$125) will do nicely. For $250 more (excluding shipping), Douglas, who goes by his Instagram handle, Ammoskunk, will work his magic.

This isn't just a cut-and-paste job. It's a complex 13-step process that requires five to seven hours of tedious labor. Heat guns, electric routers, industrial solvents and glues—these are the tools of Ammoskunk's trade. Re-stitching toe caps with a sewing awl. Fabricating "NIKE AIR" heel tabs by pouring resins in molds. This is some serious craftsmanship.

How good is Ammoskunk? "There are hundreds of people doing swaps, but only a handful of them can do what I do," he says matter-of-factly. "Not to brag, but I'm the only one who's been able to pull off a Jordan 2. You have to shave those soles out perfectly to make them fit." Don't expect a quick turn-around. Ammoskunk has a 3-month backlog.

Molly Cranna/WIRED

For those on a budget, there's a wealth of video tutorials that cover this bizarre DIY subculture in minute detail. Watching young men with Photoshop skills painting donor midsoles with Angelus Acrylic Leather Paint and fine-point "shader" brushes is quite a treat. Inside tip: Ever dreamed of bleaching the yellow out of the "icy" soles of your 2000 Laney Air Jordan 5s? Now you can. Sea Glow, a toxic chemical compound used to clean the hulls of fiberglass boats is caustic but quite effective. It's fallen out of favor, though. Legends Sole Sauce is now the go-to product for rejuvenating "piss-yellow" polyurethane.

Shoe manufacturers claim that in recent years they've improved PU formulations with additives and stabilizers that prolong the life of midsoles. "We're not making a product that lasts 20 or 30 years," says Paul Litchfield, the VP of Reebok's Advanced Concepts Group. "But we've conducted accelerated aging tests, and the shoes are lasting longer." Exactly how much longer he won't say, but it's definitely "longer." (We asked Nike about PU degradation and what might be done about it, but the company declined to comment.)

A truncated life cycle is a small price to pay for the pleasure of walking on marshmallow soles.

Vincent A. Haas, the marketing manager for performance materials at BASF, a major polyurethane manufacturer, says thermal plastic polyurethane (TPU), specifically BASF's Infinergy brand, trumps garden-variety PU. The new Adidas "Boost" cushioning system is based on this proprietary TPU. Not only does Infinergy top PU in energy return and compression set tests (94 percent vs 75 percent), Haas says it's a far more stable compound. Asked if his TPU soles will crumble, Haas replies confidently, "That problem doesn't exist." He's hesitant, however to quote an expiration date. Pressed for an answer, he gives Nike a jab. "I'll say this: 20 years from now, our shoes will still be wearable."

Adidas has an exclusive licensing deal with BASF for the time being. But foam polyurethane shoes aren't going away anytime soon. It's an inexpensive and versatile material that shoe companies are reluctant to part with. And why should they? They're focused on designing high-performance athletic shoes, not designing collectables that can be bequeathed to future generations.

Once they know about it, most people outside the hardcore sneakerhead community gladly accept the tradeoff with polyurethane. A truncated life cycle is a small price to pay for the pleasure of walking on marshmallow soles. Even some sneakerheads are rolling with it, like basketball star and Nike aficionado Nate Robinson. The 5-foot-nine veteran has worn DS/OG Nikes during playing stints for several NBA teams. Like other players who indulge in this dangerous practice, he is aware that a "blow-out" is always possible. Still, Nate "The Great" says he wouldn't have it any other way. "I like the authenticity of original Nikes," says the L.A. Clipper guard. "I wore a pair of Jordan 3s during a game that fell apart. No big deal. I just put on another pair at halftime."

If Nate does have a blow-out on the court, don't ask him for a souvenir after the game. "If my Jordans crumble, I still keep them because they're OGs. Too many childhood memories, man."

Artist Brian Jungen agrees with Robinson. His colorful sculptures and aboriginal masks, constructed from vintage Air Jordans, are a museum conservator's nightmare. Jungen advises the owners of his work (including Michael Jordan himself) to keep a stock of retro shoes on hand so that repairs can be made when necessary. Hydrolysis and oxidation, however, cause Jungen no grief. "There's something reassuring about this material not lasting forever," he says earnestly. "All art is impermanent."

1UPDATE: 3:37 ET 05/18/15. This story was updated to correct who visited Jordan Geller's "Shoezeum" in Vegas—it was Nike CEO Mark Parker, not founder Phil Knight.