It's the halfway point and the designers are hitting the road to a denim explosion. In a Project Runway throwback challenge, they'll create all-denim looks while competing in head-to-head battles where only one designer can be safe from elimination. Uncut Gems star Julia Fox - a model, actress and It girl of fashion - and designer Willy Chavarria guest judge and weigh in on the exuberant uses of denim.