In terms of stretch, it’s important to remember that there are two main types of Allbirds shoes, Wool, which has a merino wool upper, and Tree, which has a eucalyptus fibre upper. Allbirds’ Wool shoes will start as tight as they’re going to get and stretch over the course of a few weeks of wear by around a quarter of an inch or so. Allbirds’ Tree Runners shoes, meanwhile, are more rigid, and will generally remain their original size, even after a couple of weeks of breaking them in.