The Liberate NITRO™ 2 is a fast option for your short distance runs and races. It's lightweight, flexible, and leaves you free to push the limits. A simplified mono-mesh upper is teamed with a firmer NITROFOAM™ that's more responsive than v1, resulting in a shoe that's built for a tempo run and distances up to a half marathon. NITRO™: Advanced nitrogen-injected foam designed to provide superior responsiveness and cushioning in a lightweight package. PUMAGRIP: Durable performance rubber compound designed for all-surface traction.