Image copyright Invisibobble Image caption Sophie Trelles-Tvede is the chief executive of hair accessories company Invisibobble

The BBC's weekly The Boss series profiles different business leaders from around the world. This week we speak to Sophie Trelles-Tvede, chief executive and founder of the hair accessories company Invisibobble.

For most students, founding a company would probably be the last thing on their mind when they're hungover.

Back in 2011, Swiss entrepreneur Sophie Trelles-Tvede was finding her feet as a first-year student at Warwick University, but she was feeling unfulfilled.

"Studying in the UK was my dream, and I had worked so hard to get there. But all of my exams and deadlines weren't due until summer, so all of the work was back-loaded.

"We were just about to go into the Christmas holidays, but I felt like I didn't deserve them at all," she says.

To combat this "numb" feeling, Sophie, then 18, went to an "anything but clothes" night at the students' union, where partygoers wear costumes they've made out of random items.

Image copyright SOPHIE TRELLES-TVEDE Image caption Sophie started at Warwick University in 2011

Sophie, now 27, says: "As I was heading out the door, I spotted this old, disused telephone on my wall. I unplugged the [spiral] cord, and tied my hair up with it."

The "light bulb moment" as Sophie describes it, came the next morning.

"I woke up hungover, but with no headache at all, even though I had been getting them regularly. The hair tie didn't pull, or leave a dent in my hair."

Sophie called her then boyfriend, and now business partner, Felix Haffa. The two decided to work on creating a prototype - a spiral hair tie - over the Christmas break, financing the project themselves.

"We asked a guy who produced telephone cord to strip out the wire, and solder it into a round shape.

Sophie adds: "The first box was terrible! But I thought to myself: 'There's still something to this'."

Gathering feedback and tweaking the product over months, Sophie settled on transparent packaging with three spiral hair ties in each £5 ($6.25) box.

"The packaging was so important to me. I wanted buying an Invisibobble to be a fun experience - like buying an eye-shadow palette, rather than toilet paper!"

The two decided to switch to a larger producer in China in 2012 in order to produce the hair ties in bulk. They started selling products online that year, as well as to hairdressers.

Image copyright Invisibobble Image caption Invisibobble hair ties are now sold in more than 70 countries

Sales grew quickly, and Invisibobble went international in 2013. Pairing up with distributors around the world, the firm started shipping to 12 countries.

Although the company was growing, Sophie says: "People were initially really dismissive of my product. I was laughed off because it was 'just a hair accessory'.

"My flatmates would laugh at my Instagram posts about the business, or if I was creating an invoice on one of the uni computers."

But by the time Sophie's graduation rolled around in 2014, Invisibobble had an annual turnover of more than €6m ($6.6m; £5m).

"People still couldn't believe that Invisibobble could be a full-time job for me.

"In my final year, the careers counsellor told me to apply for jobs in HR after she found out that I wanted to work solely on my business."

Sophie noticed a shift in 2016, after she and her business partner Felix were listed on the Forbes Under 30 European entrepreneurs in retail list.

"That's when people started taking us seriously," she says.

Sophie says this is the moment when Invisibobble really started "strategising".

"We put a product on the market, and it was a hit. It felt super-weird. But we had never taken a moment to step back and think about the bigger picture."

A few instances of Invisibobble being copied caused Sophie to change tack. "In every market, the same thing would happen," she says. "We'd overperform, then another label creates a cheaper version.

"Now, it's too risky to just come up with an idea in the shower. We have to be the most innovative hair accessory, and we have entire teams developing the coolest products or campaigns."

Image copyright Invisibobble Image caption Invisibobble scrunchies were used by designer Marina Hoermanseder during Berlin Fashion Week last year

It seems to be paying off for the company which now has its headquarters in Munich, while the products are manufactured in South Korea and Germany as well as China.

Invisibobble, which now also sells hair bands and hair clips, reported sales of €20m ($21.7m, £16.6m) last year. It is today sold across more than 100,000 locations including in chains CVS, Walgreens and Sephora in its largest market, the US.

More than 100,000 people now follow the brand on Instagram, too. Sophie recently used the social media platform to speak out about bad working practices she saw in China during a 2018 trip.

"All of our production was running smoothly in China, our factories were fully audited," she says.

"But we thought we'd visit some [new] factories to see if we could learn anything from what other companies are doing there."

"Mothers would have children on their laps while they were soldering hair ties together, then putting labels on them for huge, multinational brands. It was heartbreaking."

After visiting eight different factories in China, Sophie decided not to explore any of them as options, sticking with Invisibobble's existing audited manufacturers. She says: "It made me realise, the most important thing is that we need to grow sustainably."

Although Invisibobble's best-selling product, its spiral hair tie, is made from plastic, the company says it's made from one single material, polyurethane. It says this makes the product fully recyclable.

"We also want people to consume less, and more responsibly. By fixing a higher price point than traditional hair ties, we try to encourage that," Sophie adds.

Having grown a successful company, Sophie now has advice for young entrepreneurs: "Start now!"

More The Boss features:

Younger entrepreneurs like Sophie have "at least two advantages", according to Vangelis Souitaris, professor of entrepreneurship at City University's Cass Business School. "They have the passion, energy and creativity of youth. Second, they have little to lose.

"They generally don't have children or a mortgage to worry about, so during or immediately after university is a good time to take the leap and found a business."

Sophie says that if you have a good idea "somebody else will do it if you don't".

"Also, if you start a business as a student, you can take a risk because you don't have to leave a full-time job to set up a company. The worst case is - it doesn't work out."