Allbirds Tree Runners Lightweight, breathable eucalyptus fiber provides next-level comfort. Cushioned midsole gives wear-all-day support. Machine-washable materials keep shoes looking like new. Worn twice! No box. If you haven't worn Allbirds Tree Runners before, they only come in whole sizes and you normally have to size up. I am usually a size 8 in shoes and sandals, and the size 9 are perfect for me.