The epiphany came not long after Abigail Forsyth had returned to work after the birth of her daughter, running Melbourne’s Bluebag chain of cafés with her brother Jamie. “My daughter Bess was 18 months old, and I’d be having a coffee in a disposable cup in the morning and she’d have her milk in a sippy cup. It got me thinking, would I ever give her milk in a disposable cup?"

Already feeling guilty about the thousands of polystyrene coffee cups her 10 cafés were sending to landfill every week, Forsyth decided that if her answer to that sort of question was ‘no’, then plenty of other people could be persuaded to drop the disposable habit too.

Five years after her epiphany, the KeepCup company – Abigail, chief executive officer, Jamie, chief operating officer – has sold 3.5 million reusable plastic coffee cups in 32 countries, and the business is turning over more than $6 million a year.

The story of how Forsyth did it is a study in the power of a simple idea, when that idea is backed by true believers.

“KeepCup has succeeded in building a story about sustainability, but you won’t see it on a billboard, or if you go to its website you won’t read about a KeepCup environmental foundation," says the managing director of Interbrand Australia , Richard Curtis (who’s not worked with the company).

“The entire brand is in the utility of the cup itself."

The reusable coffee cup had, of course, been around a long time before Abigail Forsyth came along.

The problem was its desperately uncool reputation.

“They had come out of that filtered coffee culture in the United States, where people wanted their reusable cup to be a thermos. Just in case they wanted to drink the rest of their coffee in like five hours," Forsyth explains, wincing visibly at this affront to Australia’s “light roasted" coffee culture, delivered to us courtesy of the post-war wave of Italian immigrants.

Befitting something supposed to be carried around by a truck driver from the American mid-west, Forsyth remembers that the reusable cup designs available were ungainly and ugly affairs.

“They didn’t fit under the brew head [of the café coffee machine], you couldn’t make a decent latte in them," she says.

“The barista also had no way of knowing the internal volume of the thermos, so you’d end up with too much or too little milk. They’d roll their eyes whenever someone came in with one so you’d end up with a poor customer service experience all round."

Forsyth would have to invent Bluebag’s solution to its disposable cup problem herself.

Luckily for her, the Bluebag chain provided two important ingredients for such an invention’s success.

One, they were throwing off plenty of cash. This allowed Forsyth to engage a firm of Tasmanian-born graphic designers called South Southwest, and some industrial designers out of North Melbourne called Cobalt Niche. About $5000 later, Forsyth was holding the prototype KeepCup (christened by Andy Sargent from South Southwest) in a slightly trembling hand.

The design has changed over the years, but perhaps the most important KeepCup element was there from the start. The original 8-ounce (240-millilitre) prototype mimicked the size of a standard café disposable cup, so it would not interrupt a busy barista’s production line.

“It felt like a lot of money to have spent on this crazy idea for a better plastic cup," she remembers. “Of course this was in 2009, before 3D printing. It would cost you about $50 today."

In any case, that prototype paid for itself many times over. Filled with the zeal of a born-again recycler, Abigail and her brother refined their pitch for the KeepCup by presenting it to about 200 different companies as an environmentally friendly branding opportunity.

“We were told that if you can’t sell a plastic cup off the prototype, there probably isn’t a market for it," Forsyth remembers.

The spiel was refined enough that by the time Forsyth rode her bike to a meeting with National Australia Bank (NAB) at its Bourke St headquarters, prototype KeepCup in her backpack, “all I needed was a bit of luck".

That arrived in the fact that NAB was moving many of its operations to new ‘six-star green rated’ buildings, and decide KeepCup was a good gift to staff in line with that ethos of sustainability.

“They ordered 5000, off the prototype. I remember sort of floating back downstairs and ringing my dad,’ Forsyth says.

An entrepreneur himself, with a business selling computer accessories, Forsyth says her father is always the first person with whom she shares her successes.

“My parents weren’t that thrilled when I dropped out of law to run cafés, and they were sceptical of this plastic cup thing too," Forsyth says.

“I remember I told dad the NAB news and his first words were – ‘Don’t celebrate until you get the purchase order’."

The purchase order did arrive, followed shortly by another for 5000 KeepCups from EnergyAustralia in Sydney. This early success came despite the pair still experimenting with two different pitches. One focused on the sustainability story, a grown-up version of which still appears in KeepCup’s marketing materials. With 3.5 million KeepCups now sold globally, the company invites you to imagine a situation where 80 per cent of those 3 million “environmentally conscious commuters" drink eight takeaway coffees per week. In that scenario, KeepCup users will have diverted 3.5 billion disposable cups from landfill in the past year.

“This equates to removing over 4000 tonnes of disposable cups from the waste stream and saving enough energy to power 5000 homes for a year. Furthermore, this leaves 50,000 trees left standing in a forest somewhere – that’s a lovely thought," KeepCup tells its potential customers.

Nevertheless, it was the use of funky primary colours which seemed to get most of the early buyers more excited.

“So now we pitch hard on them looking good, and hope that you keep using them because you feel good," Forsyth says.

“Once we had those sales from NAB and EnergyAustralia we had the confidence to go into full production," Forsyth says.

All that pitching also helped KeepCup win two grants of $30,000 each – one from Melbourne City Council’s Small Business, Micro Business and Social Enterprise Grant program, the other from Design Victoria – which helped towards the $500,000 cost of tooling for KeepCup’s initial production run.

The Forsyths also needed a short-term bank loan, which Abigail confesses was not from its first customer (although KeepCup has since switched to banking with NAB).

It was once the boxes of KeepCups began arriving – from the factory in Melbourne’s Lilydale that KeepCup retains to this day – that the Bluebag cafés came into their own for a second time.

“We were still our own biggest customers in the early days, and the feedback from customers was a great guide to what worked and what didn’t," Forsyth says.

The siblings soon figured out that the most important client for KeepCup, however, wasn’t a customer at all.

“It’s the floor staff in a café that have the most say in what gets ordered in, it’s a bottom-up business in that way," Forsyth says. KeepCup has long targeted baristas, including with its sponsorship of the last World Barista Championships that were part of May’s Melbourne International Coffee Expo. (KeepCup built a washing-up stand to encourage reusable cup use and help divert some of the 30,000 disposable cups it estimated would be thrown away during the four-day event).

Barista feedback has been crucial in KeepCup’s evolution.

The cups have a polyethylene lining which, in ad hoc barista taste tests, was found to make the coffee taste better than the straight polystyrene of which most disposable cups are made. That said, Forsyth admits the KeepCup will never be the equal of the ceramic cup favoured by the sit-in purists.

New sizes have been added to match the existing standards in disposable cups, so a KeepCup is less prone to disrupting a coffee production line, particularly in morning peak where every second counts. KeepCup now makes a 4 ounce (120ml) babycino size, regular (8 ounce) and large (12 ounce) editions, plus a 16 ounce to help it break into the US market.

The company also needs to stay on top of trends in what can be a frivolous market. It’s about to introduce a 6-ounce KeepCup to cater to a new craze – coming out of Melbourne, where else? – for three-quarter-sized lattes, otherwise know as “magics".

“They’re for people who want less milk and a stronger coffee," Forsyth explains.

In addition to the 20 people it now employs in Australia, KeepCup has a nine-person office in London and a five-person beachhead in the arts district of downtown Los Angeles, servicing its 26 distribution partners around the world, which are mostly café chains and/or coffee roasters.

The global push has required a transition of the KeepCup business model.

KeepCup’s supporters to date have been small café chains and boutique, independent coffee roasters. An order for 15,000 branded KeepCups from Campos Coffee founder Will Young was crucial to building momentum in the first six months of the business.

However the big Wild Bean chain became a KeepCup distribution partner in March, and Forsyth sold 15,000 cups to its Ukrainian equivalent at around the same time.

She’s not worried about losing cachet with a few hipsters.

“The true fans of KeepCup are the ones who believe, like us, that many small acts can add up to a phenomenal difference for the environment. With the KeepCups that Wild Bean sold in their first three months they diverted 98,000 cups from landfill, and that is the kind of result I’m after."

Even the world’s largest coffee chain, Starbucks , is not beyond Forsyth’s ambitions.

“At the moment they would just go and knock off a reusable cup in China; we’re not bringing them anything. But once we’ve built the brand value in the US like we have in Australia, we’ll be talking to them."

The founder of KeepCup suggests entrepreneurs should collect feedback, keep their eyes on their goal and sometimes, be careful what they wish for.

Yours to keep: Five business lessons from Abigail Forsyth

The founder of KeepCup suggests entrepreneurs should collect feedback, keep their eyes on their goal and sometimes, be careful what they wish for.

1. Don’t be afraid to share the idea you’ve just come up with

“You need all the feedback, positive and negative, that you can get. Remember, you’ve got to go out and sell this thing."

2. Your most important client isn’t always the customer

“Keeping the barista happy is so crucial to our success, even though they’re not the one paying $12 for a KeepCup. In the early days we knew that people would be less self-conscious about taking our product into a cafe if they knew the barista was going to smile and say ‘good on you’."

3. Never forget your goal

“I’ve never measured our success in cup sales, even as they’ve gone into the millions. We’re about the reuse rates and the number of disposable cups diverted. We don’t want someone to buy a KeepCup and stick it in their cupboard."

4. Be careful what you wish for

“In some ways we’ve been a victim of the success of the brand, where KeepCup is becoming a generic term for all reusable cups, including the cheap Chinese copies which leak, burn your hand and create inertia around reuse," Forsyth says. Becoming a generic name and losing the original trademark’s meaning is a danger for many successful brands, says Interbrand managing director Richard Curtis , with the Hoover vacuum cleaner company being history’s most famous victim. “However in KeepCup’s case I’d say there’s enough depth and meaning there to survive that. People interact with more than the logo," he says.

5. Turn clients into evangelists

“When a cafe makes an order for KeepCups, we give them all the ideas we’ve got for maximising sales," Forsyth says. “We encourage them to count and publicise reuse rates – they’re now as high as 6 per cent or 7 per cent in some of our independent cafes – and offer discounts to clients who bring in one of our cups. A branded disposable polystyrene cup can cost a small cafe as much as 25¢, so there’s real savings there. But we know that cups aren’t their core business – coffee is, so the other important aspect is not interfering with their ability to pump out those lattes."