“HIPPIE STYLE ALWAYS comes back,” explained Elijah Funk. He should know. Mr. Funk, 28, and his friend and business partner Alix Ross run Online Ceramics, a two-year-old Los Angeles-based brand that has gained currency for its Grateful Dead-inspired T-shirts. The designers and their work were recently showcased in a GQ Style magazine spread, and their shirts (whose trippy graphics feature, say, a peace sign passing through a basketball hoop or a sun wearing sunglasses) are sold at boutiques like Union in Los Angeles, next to high-end wares from designers like Raf Simons and Thom Browne.

John Mayer arriving at LAX in a Grateful Dead T-shirt back in 2015, the same year that he joined Dead & Company. Photo: AB Images / Barcroft Media

Online Ceramics’s success is part of a larger Deadhead infiltration of higher fashion. Tie-dyed pieces from designer labels like Amiri, Saint Laurent and Balenciaga are pouring into stores for spring, denim cutoffs are back in and decades-old Grateful Dead shirts are fetching hundreds of dollars at vintage stores.

“The Grateful Dead has gone very mainstream,” said Darryl Norsen, 37, a longtime fan and writer based outside Boston, who’s penned a Grateful Dead column for the music site Aquarium Drunkard since 2013. When Mr. Norsen looks at the crush of Grateful Dead fashions showing up out there, even on unlikely celebrities, he just wonders where they all were 20 years ago. Back then, a few of his friends were quietly screen printing bootleg T-shirts, but the Deadhead influence on clothing “certainly wasn’t [being felt] to the extent that it is now.”

So how did the Dead go from hide-it-from-your-girlfriend lame to cool enough for a full-blown GQ spread? Some credit is due to Dead & Company, the psuedo-revival of the band (with John Mayer subbing in for Jerry Garcia) that has been touring since 2015, but there’s a lot more to the story than that.

Two T-shirts designs from Online Ceramics, a two-year-old label known for their zany (and surprisingly sought after) Grateful Dead inspired shirts. Photo: Danny Kim/The Wall Street Journal, Styling by Jill Telesnicki

In 2015, Mason Warner, a Philadelphia-based graphic designer and devoted fan (he traveled with the original band from 1989 to ’94) started @FromTheLot, an Instagram account dedicated to cataloging the many bootlegged, fan-made Dead T-shirts, some dating back decades. Today, @FromTheLot has nearly 28,000 followers ranging from Sarah Andelman, who owned the now-closed iconic Parisian fashion boutique Colette, to Atlanta Hawks forward Miles Plumlee to film director Max Winkler. Showcasing many versions of dancing bears, skeletons and lightning-bolt-emblazoned skulls (the band’s famous “Steal Your Face” logo), Mr. Warner’s scrollable archive exemplifies how Dead iconography has found a second life on social-media platforms.

This Deadaissance isn’t just happening on the internet: Last year, film director Amir Bar-Lev released “Long Strange Trip,” a 238-minute documentary (now streaming on Amazon) covering the Dead’s career. A romantic vision of the life on the road, the film portrays blissed-out fans in tie-dyed tops, floral shorts and pale bluejeans. Any given frame of the movie could be pinned to the mood-board of a designer intent on turning out hippie-dippie designs--see Russian designer Gosha Rubchinskiy’s swirling tie-dye sweatshirts, J.W. Anderson’s above-the-knee jorts or Missoni’s rainbow-plaid trucker jacket.

Such labels are clearly hoping to tap into the carefree ethos of the Dead. When we’re chained to our smartphones and bombarded with bleak news alerts and emails from the office at all hours, laid-back liberation appeals. “It is a fun little break from stuff that otherwise might make you pretty bummed out,” said Jeremy Dean, a graphic designer who’s been making Dead-inspired T-shirts since 2012.

The fall 2018 runway shows had some seriously Deadhead-esque fashions like Russian designer Gosha Rubchinskiy’s swirling T-shirt, Missoni’s wavy sweater and Burberry’s heart-shaped tie-dye tank top.

When Mr. Dean started out, he made the shirts for himself: “I just wanted to wear something weird and goofy,” he said. Apparently, others do too. When he releases shirts that riff on, among other things, the Dead’s Steal Your Face logo, they sell out in a matter of hours on his website, he said.

What Mr. Dean and his peers are offering, particularly to a younger generation that wasn’t there the first time around, is a wearable token of the Dead lifestyle. Jerry’s gone. The ’60s are never coming back. Your cellphone keeps buzzing with that message you should’ve replied to days ago. But when you slip on a tie-dyed sweatshirt or one of Mr. Dean’s grin-inducing T-shirts, you can feel for a moment like you’re on the road, without a worry in the world.

Write to Jacob Gallagher at Jacob.Gallagher@wsj.com