Flame resistant fabrics formed with a combination of body yarns and stretch yarns that exhibit excellent physical and thermal properties. The body yarns are formed at least in part with flame resistant materials. The stretch yarns are corespun yarns having an elastic core surrounded by a fiber sheath formed at least in part with flame resistant materials. The fiber sheath protects the elastic core from direct exposure to heat and flame that would otherwise cause the core to degrade or melt.