Chinese scientists announced they’ve invented a new kind of coating for aircraft and other weapons that’s virtually undetectable by radar.

This new, lab-made “metamaterial,” in essence a very fine mesh with microscopic etchings, could shrink the radar signature of a fighter jet, warship, or missile by a thousand times, claimed the scientists at the Chengdu-based Institute of Optics and Electronics, part of the Chinese Academy of Sciences.

If the Chinese team led by professor Luo Xiangang is telling the truth and their metamaterial works like they’ve claimed, China might seem poised to become the world leader in stealth technology, leapfrogging the United States and effectively canceling out a major American military advantage.

But there are good reasons to be very skeptical.

“ As with many new technologies, there is sometimes a little hype when reporting preliminary results. ” — Sir John Pendry, professor at Imperial College London

Metamaterials such as the Chinese mesh are not exactly new. But they’re new enough that their promise often exceeds their actual performance and usefulness. “As with many new technologies, there is sometimes a little hype when reporting preliminary results,” Sir John Pendry, a professor at Imperial College London, told The Daily Beast.

Pendry knows what he’s talking about. Back in the mid-1990s, he invented the first metamaterial. A metamaterial is any man-made substance—an exotic metal alloy, for example—that displays properties not normally found in nature. Like the ability to disappear to the naked eye, or on radar.

Luo and his colleagues at the Institute of Optics and Electronics didn’t actually make any of their stealth mesh. Rather, they created a mathematical model that describes a metamaterial with incredible stealth qualities.

In a mid-July official notice first widely reported by the Hong Kong South China Morning Post, the Chinese researchers claimed their mesh could reduce, by up to a thousand times, the radar signature of an object across a swath of the electromagnetic spectrum from 0.3 to 40 gigahertz.

Many military radars operate at around 10 gigahertz, meaning the Chinese metamaterial in concept works in exactly the frequency that’s most important for American air defenses. The Institute of Optics and Electronics did not immediately respond to a request for comment.

“The reflection and transmission electromagnetic wavefronts can be reshaped by the local phase control of the metasurfaces,” the researchers claimed in a separate announcement. “This approach uses the random distribution of local reflection phases of unit cells, which enables diffuse electromagnetic scattering.”

In plain English, the scientists said they etched tiny, random grooves in a special metal. The grooves scatter a radar wave in a million directions. Very little of the wave would return to the emitting sensor. “Consequently, the radar cross section would be dramatically reduced,” the Chinese team asserted.

Cover a plane, missile, or ship in a mesh based on Luo and company’s model, and in theory it would all but disappear from radar scopes. South China Morning Post cited a “stealth technologist” from Fudan University in Shanghai, claiming the new technology could “fool all military radar systems in operation today.”

That’s exactly the outcome the Chinese People’s Liberation Army wants, and has been spending big to obtain. “China continues to seek niche technological developments that could potentially revolutionize the PLA’s military operations by providing a credible asymmetric edge in regional flashpoints in East Asia,” Michael Raska, a foreign policy expert at Nanyang Technological University in Singapore, told The Daily Beast.

But the concept of a new radar-evading mesh doesn’t necessarily, or immediately, translate into any kind of military edge. For starters, there are other ways of achieving stealth. The overall shape of a plane or ship can greatly reduce its radar signature. Special radar-absorbing materials capture radar waves instead of reflecting them.

The U.S. military and the PLA both operate stealth warplanes. America’s force of hundreds of stealthy F-22s, F-35s, and B-2s greatly outnumbers China’s own fleet of a few dozen radar-evading J-20s.

True, the mesh could give weapons-developers more and better options for designing stealthy ships, planes, and missiles. Assuming it actually works, that is. The Chinese announcements lack detail and, more importantly, proof . “I took a look at the references, but unfortunately there is nothing technical to go on so I cannot comment on the claims of these people,” Pendry said.

Nor is it clear that Luo’s mesh is actually all that special. For two decades now researchers in universities, government labs, and private companies all over the world have been tinkering with metamaterials and, in a few cases, actually making useful devices out of the weird substances.

Inspired by Pendry’s work, the U.S. Air Force got involved in metamaterials as early as 2000. The Air Force was particularly excited by the development of lenses made of metamaterials. In contrast to conventional, curved glass lenses, these “superlenses” can be made tiny and flat and yet still outperform the old glass models. The Air Force did not immediately respond to a request for comment.

“ Overall, China is still more of a ‘fast follower,’ always playing technology catch-up. ” — Michael Raska, foreign policy expert at Nanyang Technological University, Singapore

It was a small step to make metamaterials that can capture light better than conventional materials can. The implications are huge for the energy industry. In 2017 Lockheed Martin, America’s top weapons-manufacturer, invested in a metamaterials company, officially in order to develop new ways of harvesting solar power.

It would be surprising if Lockheed and other U.S. defense firms weren’t also developing metamaterials for military use. “Western armaments producers continue to outpace China when it comes to most military technologies,” Raska pointed out. A Lockheed spokesperson did not immediately respond to a request for comment.

“Overall, China is still more of a ‘fast follower,’ always playing technology catch-up,” Raska added. If China has ideas for a stealthy metamaterials, it’s likely America does, too. And China’s supposed new stealth advantage is, at best, a wash.