Engineered stretch knit upper: Improves breathability External back heel counter: Helps keep the foot stable and provide a more comfortable stride 4D GUIDANCE SYSTEM feature: Helps create adaptive stability for a more balanced stride Rearfoot PureGEL technology: Helps provide lightweight cushioning and softer landings FF BLAST PLUS ECO cushioning is made with approximately 20% bio-based content and helps provide cloud-like comfort: Only ever worn to try on. Never worn outside.