Allbirds, the B Corp-certified Californian brand of sustainable sneakers and apparel, has filed for a confidential initial public offering (IPO), according to WWD. Such a filing allows a company to keep details of its business performance and the terms of the transaction secret until 15 days before the IPO takes place. In April, the DealBook newsletter of The New York Times wrote that the company was interviewing banks in preparation for an IPO. Allbirds was last valued at around $1.7 billion in a $100 million Series E funding round held in September 2020. Starting in 216 with the launch of ahtletic footwear made with wool uppers, the company now has a full line of shoes and clothing made with wool and a variety of tree fibers. While making availabile its methodology to other firms, Allbirds recently partnered with Adidas on a low-carbon running shoe.