Allbirds

The merino wool used in their shoes is ZQ-certified, which means it meets stringent standards of sustainable farming and animal welfare. Their superfine merino wool also requires 60% less energy to produce than typical synthetic materials used in shoes.
Source: ZQ Merino (2019)

This company is a member of the Sustainable Apparel Coalition, a multi-stakeholder initiative launched in March 2011 by a group of global apparel and footwear companies and non-profit organizations (representing nearly one third of the global market share for apparel and footwear). The Coalition's goals are to reduce the apparel industry's environmental and social impact, and to develop a universal index to measure environmental and social performance of apparel products.
Source: Sustainable Apparel Coalition (2020)

This company has a number of sustainability claims on its website including use of recycled packaging, donating lightly used Allbirds to Soles4Souls, and using natural materials.
Source: company website (2019)