Invisible pattern can put a stop to counterfeit fabrics

Chalmers University of Technology researcher Christian Müller has produced a thread with unique optical properties which can be used to create invisible patterns in fabrics that are only visible under polarised light. From a long-term perspective, Christian Müller's discovery could also be used to manufacture ‘smart textiles’, such as clothing that changes colours based on electrical charge.

According to Swedish Customs, trade in counterfeit and pirated goods has exploded the past few years in Sweden, the EU and globally. The situation impacts companies, their employees and unknowing consumers. It is often difficult to see the difference between a genuine garment and a knockoff.

Christian Müller, researcher in polymer technology at Chalmers University of Technology, has found a solution to the problem. He has created a partially invisible thread made of polyethylene and a dye molecule that absorbs visible light. The thread can be weaved into a pattern that is invisible to the naked eye, but which can be seen using a polarisation filter.

“The production process itself is uncomplicated,” he says. “Clothing manufacturers could start using the thread right away to put a signature pattern in their garments. The equipment needed to see the pattern is fairly simple and is already in place at Swedish Customs, for example.”

The invisible thread can be created using several different dye molecules and several different synthetic fibre textiles such as nylon. The dye molecule can also be bonded to natural fibres such as wool and silk. The technology can be used both for clothes and for different types of expensive specialty fabrics such as the textile used in vehicles and caravans.

The idea is for a brand to be associated with its own special combination of textile fibres and dye molecules. The thread is easy and inexpensive for a company to produce.

“It is very difficult for pirate manufacturers to copy the unique combination,” says Christian Müller. “They can obtain the equipment needed to read the pattern and ascertain the optical spectrum produced by a specific signature, but they cannot know which combination of components will produce the specific spectrum. And there are loads of different dye molecules available for use.”

He published his results last year in the Applied Physics Letters scientific journal. Prior to that, it was not known that a pattern can be created in textile that is part of the actual fabric and that is only visible under polarised light. There is, however, a similar technology available for creating invisible patterns on banknotes, which is used in Switzerland, for example.