Xero Shoes Mens Hfs Running Shoes - Zero Drop, Lightweight & Barefoot Feel Yellow Vibe, 13The HFS is my favorite running shoe BY FARWhy HFSWell, it could be Hyper Fast Shoe, or the Highly Flexible Sole, or Happy Face Shoe, or what many people say when they feel the light weight and comfort: H___ F____ S___There are as many answers as there are thin..