Traditional capacitors such as those in a radio could store only a tiny amount of energy. With the advances in science in recent years, scientists were able to increase their energy storage significantly with the hope to rival or even replace batteries with the so called supercapacitors.

The new supercapacitor material developed by the Chinese team was soft and expandable. It could stand a pull to three times its original length, according to their paper published on the academic journal Advanced Materials last week.

Professor Wei Zhixiang, a correspondent author of the paper with the National Centre for Nanoscience and Technology in Beijing, said the latest material they developed was “even better” than the earlier version which they reported in the paper.

“With the advancement of this technology, it is very possible to develop products that can come into close contact with the skin, such as (a) bikini and bra.”

“The material is getting softer, easier to manufacture, more comfortable to wear,” he said.

“Underwear is definitely one of our dreams,” Wei added.

“To make the underwear we face the highest requirement for safety, reliability and comfort, but we like sexy challenges.”

Unlike elastic supercapacitors developed before, which were mostly very thin films, the new material could be nearly a centimeter thick.

The extra thickness enabled the new supercapacitor to store more energy with higher strength to withstand external shocks as well.

The researchers bended the gel-like materials more than a thousand times and did not detect any crack or decrease of its energy storage performance.

The new supercapacitor could even be transparent.

The research team developed a new fabrication technology which allowed a very thin film of electrolytes to be sandwiched between two thick layers of hydrogels. The conductible hydrogels would facilitate free movements of electrons to and from electrolytes during charging or discharge.

The simple structure paved way for mass production in the future, according to the scientists.

The “new conceptual flexible supercapacitor... exhibits superior electrochemical performance and mechanical flexibility” which would be particularly useful for wearable devices, the researchers said in the paper.

Some female customers were offended by the idea of a bra charger.

“I bet it will increase the risk of breast cancer, with a supercapacitor over (the) chest,” said a woman in Beijing who declined to be named due to the sexual sensitivity of the issue.

But others welcomed the innovation on underwear. “I won’t mind trying,” said a female resident in Shanghai.

The new supercapacitor in lab was not immediately wearable for everyone yet, Wei cautioned.

Wei said he and colleagues were trying to overcome some remaining obstacles that got in the way of the mass production of the new materials.

The coating gel, for instance, would need to pass stringent bio-safety evaluations as certain people might be allergic to the material; and the supercapacitor inside would also need extensive field tests to prove their strength against daily wear.

There was also room for improvement. A capacitor could be charged up rapidly, sometimes in the blink of an eye, but it can also release the energy just as fast, and scientists were still exploring ways to prolong the discharge time.

Though with much more room for energy storage than traditional capacitors, supercapacitors at present still fall short compared to batteries in terms of energy storage capacity.

Farad was a unit to measure the ability of a body to store an electrical charge, and the new material developed by the Chinese team achieved a storage capacity less than half a farad per square centimetre,

That meant to charge up an iPhone with a bra made of the material, the cup-size would be larger than a basketball.

And unlike normal fabrics, the gel-like supercapacitor was air-tight without tiny holes for skin to breathe and sweat off.