Today’s solar panels are rigid and bulky. There’s nothing so wrong with that when they’re in the middle of the Arizona desert, but that bulkiness doesn’t translate to powering an iPhone or Fitbit.

To bring the sun’s power to wearables requires a new kind of solar cell, one that’s lightweight and water-resistant. As researchers at the University of Tokyo and Japan’s RIKEN research institute describe Monday in the scientific journal Nature Energy, their newly created cell could be just what’s needed.

“Our devices will be able to be integrated onto the clothing, attached onto the shoulders or backsides, or onto our hats,” RIKEN researcher Kenjiro Fukuda tells Inverse. “And these power sources can supply enough electrical powers to [Internet of Things] devices such as sensors, or maybe iPhone or smartphone systems to supply charge to the smart devices.”

The idea of solar clothing isn’t all that new; Tommy Hilfiger, for instance, rolled out limited-edition jackets in 2014 with their very own solar panels placed on the back. But there’s a reason those jackets never got brought back for a full production run: The cells were too big and hefty to work as much of anything other than an expensive novelty.

Maybe the most successful example of solar clothing is explicitly expensive haute couture: Dutch designer Pauline van Dongen released a line of dresses in 2014 that incorporated solar cells. Her collaborator, physicist Gertjan Jongerden, told Wired why the dresses couldn’t hope to move much beyond the runway.

A solar-powered dress: Fashionable, but not especially practical. Pauline van Dongen

“If you look at a solar panel system on a house it’s mounted with structures you can’t do that with clothing,” he said. “The ideal wearable portable solar cell would be a piece of textile. That exists in the lab but is not a sellable product.”

This new research from the RIKEN and Tokyo teams has taken that textile a big step forward from lab curiosity to actual product. What they have done is create a cell so small and flexible that it could, in time, be seamlessly woven into our clothing, rather than awkwardly placed on the outside of a jacket.

These solar cells are phenomenally thin, measuring just three millionths of a meter in thickness. Given a special coating that can let light in while keeping water and air out, the cell was able to keep efficiently gathering solar energy even after being soaked in water or bent completely out of its original shape.

“I believe that our result is the first-time demonstration of achieving the high-performance, high-efficiency energy conversion, and the waterproof properties and stretchability,” says Fukuda.

An example of the lightweight solar tech. RIKEN

This is a relatively basic proof-of-concept for the material, with the Tokyo and RIKEN teams focused just on fundamental research, not commercializing the technology. But this new material ticks all the boxes required of a wearable solar cell — long-term resilience to environmental hazards, energy efficiency, and the kind of flexibility that would make it not a total hassle for people to wear.

If Fukuda or other researchers are indeed able to develop these wearable solar cells further, it could mean you wouldn’t need to worry about charging your iPhone or Fitbit while walking around — either the devices could charge directly, or they could draw power from solar collectors on your clothes. Fukuda says clothing companies will be just as essential as tech companies in developing these solar-powered textiles.

A diagram of the solar cell proof-of-concept.

That said, solar cells are just one part of a larger system needed to give you power on the go, and Fukuda says there are still unanswered questions about how best to store the energy that such cells would collect.

“We don’t know if our technology is the best solution to achieve stretchable power source systems,” he says. “Of course solar cell systems cannot charge, solar cells are not the battery. So we need some kind of battery systems in the real diverse applications.”

To be truly wearable, thin, flexible, waterproof solar cells will need their very own thin, flexible, waterproof solar cells. As ever, one potential breakthrough soon demands another.

If you liked this article, check out this video of a smart-jacket that changes its temp based on the weather.