Puma EXPLORE NITRO 2 The Puma EXPLORE NITRO 2 men's hiking shoes are designed for challenging terrain. The powerful PUMAGRIP ATR rubber compound is engineered for exceptional traction on ice, mud, and unstable surfaces. Nitro boots contain NITROFOAM™ foam, which is impregnated with nitrogen and is designed to provide superior response and cushioning in a lightweight package. Puma EXPLORE NITRO 2