Ideal for both special occasions and everyday outfitting, the Millie is a flat slingback sandal with an adjustable ankle strap and lattice upper. Ideal for both special occasions and everyday outfitting, the Millie is a flat slingback sandal with an adjustable ankle strap and lattice upper. Founded in 2009, Reformation is a revolutionary lifestyle brand combining stylish, vintage-inspired designs with sustainable practices. With each limited-edition collection, the LA-based brand empowers individuals who want to look beautiful and live sustainably.