So, crocs are back, otherwise they will never go out of style. Is this camping? comfortable? Nostalgia? We are not sure. But we at Scienceline love our Crocs, whether it’s the sparkly pink pair that Lyric Aquino wore front row to a Harry Styles concert, or the blue pair that Delaney Dryfuss wore to the trendy restaurant in Martha’s Vineyard. Some of our favorites are now collaborating with Crocs like Bad Bunny, the Cars movies and 7-Eleven.
Iconic clogs have been around for 20 years, but during that time we never thought about what they were made of. Once this question comes into our mind, we cannot get rid of it. So, let’s take a closer look at the chemistry of Crocs and consider how we can change its composition to reduce the company’s environmental footprint.
It’s hard to find a straight answer on the internet. In some articles they are called rubber, in others – foam or resin. Many argue that they are not plastic.
At the most basic level, Crocs are made from the patented Croslite material. Dig a little deeper and you’ll find that Croslite is mostly polyethylene vinyl acetate (PEVA). This material, sometimes simply referred to as EVA, belongs to a class of compounds called polymers — large molecules made up of smaller, repeating molecules bonded together. Its chemical composition comes from fossil fuels.
“Alligators are definitely plastic. There’s no doubt about it,” says Michael Hickner, a materials scientist at Pennsylvania State University who specializes in polymers.
He explained that plastic is a broad category, but it usually refers to any man-made polymer. We often think of it as the smooth, pliable material used to make takeout containers and disposable water bottles. But styrofoam is also plastic. The same goes for nylon and polyester in your clothing.
However, it’s not wrong to describe Crocs as foam, resin or rubber – basically all of the above. These categories are broad and imprecise, each dealing with different aspects of the chemical origin and physical properties of Crocs.
Crocs isn’t the only shoe brand that relies on PEVA for its comfortable soles. Until the advent of PEVA in the late 70s and early 80s, according to Hickner, shoe soles were tough and unforgiving. “They have almost no buffer,” he said. “It was very hard.” But he says the new lightweight polymer is flexible enough to be a hit in the shoe industry. Decades later, Crocs’ innovation was to make all shoes from this material.
“I think the special magic of Crocs is the craftsmanship,” says Hickner. Unfortunately, Crocs doesn’t reveal much about how Crocs are made, but the company’s patent documents and videos suggest they use a common technique called injection molding, a process responsible for both plastic silverware and Lego bricks. Like a hot glue gun, an injection molding machine sucks in hard plastic, melts it, and extrudes it through a tube at the other end. The molten plastic enters the mold, where it cools and takes on a new shape.
The hot glue itself is also usually made from PVA. But unlike hot glue, the Croslite polymer will be saturated with gas to form the foam structure. The result is a breathable, loose, waterproof shoe that both supports and cushions the sole of the foot.
The process will soon change slightly to make plastic shoes more environmentally friendly. In their latest sustainability report, Crocs stated that one pair of their classic clogs emits 2.56 kg of CO2 into the atmosphere. The company announced last year that they plan to halve that number by 2030, in part by using plastics made from renewable resources rather than fossil fuels.
The new bio-based material, called Ecolibrium, was first developed by Dow Chemical and will be made from “vegetable sources such as crude tall oil (CTO), not fossil sources,” a Dow spokesperson said in an email. Tall oil, a by-product of the wood pulp production process used to make paper, gets its name from the Swedish word for pine. The company is also evaluating other plant-based options, their spokesperson said.
“Any bio-based option considered by Dow must be recovered as a waste product or as a by-product of the manufacturing process,” they wrote.
Crocs declined to clarify if they have started using Ecolibrium in their shoes. We also asked Crocs what percentage of their plastics will come from renewable sources by the end of the decade, initially thinking they were planning a full transition. The spokesperson responded and elaborated: “As part of our goal of achieving net zero emissions by 2030, we aim to reduce emissions from a couple of products by 50% by 2030.”
If Crocs does not currently plan to fully switch to bioplastics, this may be due to limited prices and availability. Currently, various bioplastics are more expensive and less efficient to manufacture than conventional plastics. They are new and compete with “very, very established” traditional processes, says Jan-Georg Rosenboom, a chemical engineer at MIT. But if the bioplastics industry continues to grow, Rosenboom expects prices to fall and availability to increase due to increased production scale, new technologies or regulations.
Crocs also plans to use other technologies to reduce carbon emissions, such as switching to renewable energy, but according to their 2021 report, this transition will not occur until the second half of this century. Until then, the bulk of the reduction will come from offsetting some fossil fuel-based plastics with renewable alternatives.
However, there is one glaring problem that this bio-based plastic cannot solve: where shoes go after they are worn out. Alligators are known to be long-lived. On the one hand, this is the exact opposite of the fast fashion problems that the industry is suffering from. But on the other hand, shoes end up in landfills, and biodegradability does not necessarily mean biodegradability.
“You know, Crocs are indestructible, which creates sustainability issues,” Hickner said. He suggests there may be more than a few crocodiles in the Pacific Garbage Patch.
Hickner explained that while most PEVA can be chemically recycled, it cannot be done along with other household recycling. Crocs may have to create their own recycling stream, recycling old shoes to make new ones.
“If Crocs wanted to make a difference, they would have a recycling program,” said Kimberly Guthrie, who teaches merchandising and fashion sustainability at Virginia Commonwealth University.
Crocs has partnered with online thrift retailer thredUP to find a new home for last season’s clogs. Crocs is promoting this partnership as part of its commitment to reducing the amount of shoes that end up in landfills. When you ship used clothes and shoes to a consignment online store, you can sign up for Crocs Shopping Points.
ThredUP did not respond to a request to find out how many pairs made it to thrift stores or were sold to new wardrobes. However, some people give away their old shoes. Searching thredUP finds a wide variety of Crocs shoes in a wide variety of colors and sizes.
Crocs also claims that they have saved more than 250,000 pairs of shoes from the landfill over the past five years through their donation program. However, this number is the reason the company donates unsold pairs of shoes instead of throwing them away, and the program does provide shoes to those who need them. However, despite Crocs’ commitment to sustainability, the company continues to encourage its Crocs Club members to come back for the latest in durable plastic clogs.
So what does this leave us with? Hard to tell. We feel a little better about missing out on our sold-out, glow-in-the-dark collaboration with Bad Bunny, but not for long.
Allison Parshall is a science journalist with a particular passion for multimedia storytelling. She also writes for Quanta Magazine, Scientific American and Inverse.
Delaney Dryfuss is currently the Editor-in-Chief of Scienceline and a researcher for Inside Climate News.
Love your crocodiles, but some are too expensive to afford. Please send me your newest pair, size 5. I have been wearing my last pair for many years. Take care of the environment and live well.
I just hope they are as good as they are now because their softness seems to be the only thing I can wear to work due to my arthritis and any other issues that happen to my feet. I’ve tried a lot for foot pain etc. Orthotic insoles… don’t work but it’s me can’t wear shoes or I haven’t found anything suitable for me and every time I walk they press on the ball of my foot, and I get electrocuted or something like that. it feels like there’s something in there that shouldn’t be there…i just want them to be as soft as the rest so i can keep working
After reading this, I thought Crocs would ruin their product. These are the best shoes on the market right now in terms of comfort and support. Why cheat success and ruin a good thing. I’m worried about crocs right now, as far as I know I won’t be able to buy them anymore.
I was at the beach in Oregon pulling two seaweed alligators. Obviously, they were in the water for a long time, as they were covered with marine life and did not break at all. Before, I could go down to the shore and find sea glass, but now I can only find plastic – large and small fragments. This is a big problem.
I need to know who is the biggest manufacturer of these shoes, we make shoe decorations, we sell more than 1000 pairs per month, we are in short supply now
It’s hard to tell if any of these comments are legitimate or just trolling bots. To me, sustainability at Crocs is like a group of billionaires signing the Giving Pledge and giving away half their fortune. None of them are actively involved in this, but they have received a lot of publicity for their statements. Crocs Inc. reported record annual revenue of $3.6 billion, up 54% from 2021. If they are genuinely interested in having companies take responsibility for the true value of their shoes, the money is already there for sustainable investment. As the younger generation embrace these footwear and sustainability, Crocs could become an MBA legend if they pay attention to changing consumer trends. But making those big leaps can be extremely difficult, as investing in costly resilience measures is diametrically opposed to returns for shareholders/investors in the short term.
A project of the Science, Health, and Environment Reporting Program of the Arthur L. Carter Journalism Institute at New York University. Garrett Gardner theme.