They’re the Stanley Cup Champions. And That’s a Lot of Mugs.

The Stanley Tumbler, this year’s smash hit, is, at first glance, a win for the planet.

It’s durable. It’s reusable. Unlike the throwaway plastic bottles it’s meant to replace, it doesn’t generate mountains of plastic trash.

But the craze has sparked some less-than-sustainable behavior. People boast about owning dozens of them. When Target released special editions, including a much-coveted Starbucks version, it caused a mini stampede.

Some trend forecasters say the fad is already over. “Some millennials or Gen-Z are already embarrassed to carry a Stanley,” said Casey Lewis, who writes the trendspotting newsletter, After School. “And we know what’s going to happen,” she said. They’ll sit unused, gather dust on a shelf or in a basement, or “worst case scenario, they’ll end up in landfills.”

Stanley mania is a story of how marketing, influencers and the power of social media converged to produce a cultural phenomenon. Stanley sold an estimated 10 million Quencher” water tumblers in 2023, andthe company’s total sales for that year is expected to have reached $750 million, up from less than $100 million in 2020. The #StanleyCup hashtag has been viewed billions of times on TikTok.

But the trend is also an example of how a growing universe of eco-conscious products — things originally marketed to be sustainable — can morph into a catalyst for simply buying more, potentially canceling out environmental benefits. Entranceways have become cluttered with totes meant to save us from the scourge of single-use plastic bags. Cupboards are accumulating odd gadgets, like collapsible steel straws or reusable food containers, meant to cut down on the single-use kind.

“The point of a reusable mug is that, theoretically, you only need one. And you’re replacing dozens or even hundreds of single-use cups with that one reusable mug,” said Sandra Goldmark of Columbia University’s Climate School. But if a person buys lots of those mugs, “you’ve got a lot of water-drinking to do,” she said, to make up for the environmental impact of manufacturing them.