Abigail Forsyth was told her business idea was "stupid".
Now the Melbourne entrepreneur is making millions selling her product around the world, as one of a growing number of businesses combining profit with positive change.
KeepCups, once the daggy accessory of sustainability geeks, have become seriously cool thanks to a shift in consumer thinking - and business is booming.
In the past month, Ms Forsyth said, demand for the reusable plastic coffee cups spiked dramatically after ABC documentary series War on Waste, starring The Chaser comedian Craig Reucassel, hit our screens.
"We have been absolutely smashed, inundated, since that aired," she said, referring to an episode that drew attention to the fact most disposable coffee cups - even paper ones - cannot be recycled.
"Our internet sales have quadrupled, our inquiries have quadrupled, cafes have called us saying they've run out already," Ms Forsyth told news.com.au ahead of her talk at the Chartered Accountants Business Forum in Sydney on Tuesday.
"Also, people who have had a KeepCup and haven't been using it have brought it in again and re-engaged with the habit."
It's just the latest coup for a family-run Australian venture that has grown from a simple idea into a global business.