Vivobarefoot Primus Trail FG 3.5 Women's Insignia BlueRun and roam wild Built for trail running and adventuring closer to nature The Primus Trail 3. 5 FG is for runners who live for the end of the road. These all terrain trainers are light and flexible enough to move freely, and tough enough to run wild on rough, rocky ground. Made with recycled, vegan*, high performance materials. We're on a mission to create a fully circular shoe a new Vivo made from an old one, which can in turn be made into another.