The Reformation Callie Tank is a medium-weight cotton sweater knit with a round neck, designed to be fitted throughout. The Reformation Callie Tank is a medium-weight cotton sweater knit with a round neck, designed to be fitted throughout. 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.