THIS MEN’S SHOE IS FOR: The Glycerin Stealthfit GTS 21 is for runners who want supreme softness, do-it-all design and added support from the GuideRails holistic support system. This Brooks Glycerin Stealthfit GTS 21 has been granted the APMA Seal of Acceptance. Predecessor: Brooks Glycerin Stealthfit GTS 20. SUPREME SOFTNESS: Now with even more super-soft nitrogen-infused DNA LOFT v3 cushioning that is optimized to be lightweight, responsive, and durable with plush comfort. GREAT SUPPORT: The Glycerin Stealthfit GTS 21 is the more supportive version of the Glycerin Steathfit 20. The innovative GuideRails holistic support system supports your body in its natural motion path while keeping excess movement in check. SECURE, ADAPTABLE FIT: Updated flat knit upper Stealthfit construction offers a blend of stretch and compression for a closer fit which provides seamless structure, breathability and adapts to the movements of your foot. BREATHABILITY: Flat Knit upper provides a seamless fit that allows for maximum breathability to keep your feet comfortably cool. With excellent support, supreme softness, and an adaptive fit, this shoe offers miles of comfort. Featuring GuideRails support, soft nitrogen-infused DNA LOFT v3 cushioning, and our comfortably snug Stealthfit construction.