Former All White Tim Brown's footwear company has sold 1 million pairs of Allbirds shoes.
That means the merino wool shoes, worn by Prime Minister Jacinda Ardern during her fashion shoot for Vogue magazine, have flown off the shelves at almost a pair a minute since they went to market two years ago.
The San Franciso-based company also announced overnight that it was launching a range of shoes made from trees.
"Crafted from a textile that Allbirds engineered using eucalyptus pulp, our tree collection creates a cooling effect by wicking away moisture and, in concert with a silky-smooth mesh construction, delivers unmatched breathability and supreme comfort," the company said.
The latest range, which the company said is made from its "most sustainable material to-date" - is manufactured with eucalyptus fibres, which Allbirds said will require only 5 per cent of the water and a third of the land traditional footwear materials use.
"The introduction of our revolutionary tree collection marks a major moment for Allbirds in our quest for a more comfortable and sustainable future," Brown and co-founder Joey Zwillinger said.
"This material doesn't compromise for comfort or for the environment, and we're excited to challenge industry norms via material innovation once again."
The tree-based shoes, according to Allbirds' website, will retail for $160 - the same price as its merino footwear.
Allbirds began with a research grant from New Zealand's wool industry, and an initial Kickstarter campaign in 2014.
In September last year it raised US$17.5 million ($24m) through US investment firm Tiger Global Management, adding to the US$10m raised in previous funding rounds since 2015, and giving it money for further research and development into novel, sustainable materials, as well as to expand internationally and grow its retail footprint in New Zealand and the US.
It is the largest direct-to-consumer footwear brand in the world at the moment, and Brown said last December that it was profitable, although he declined to provide details.
Additional reporting: BusinessDesk