synthetic-and-rubber Imported Rubber sole Go Further: Our original Altra EGO foam is designed to provide added energy return and a responsive, yet soft, comfortable feel. Get Comfortable: Signature Altra Balanced Cushioning and FootShape toe boxes allow your toes to spread and encourages proper, low-impact form throughout your run Push Yourself: InnerFlex midsole technology ensures increased flexibility and performance Lock In: The sock-like engineered knit upper keeps your foot comfortable and locked in