Women's Brooks® Glycerin Stealthfit 21 :: Looking to increase speed or distance? Your updated Women's Brooks Glycerin Stealthfit 21 is crafted to accommodate, with custom-fit contouring that feels one with your foot. Packed with updates such as the new RoadTack rubber for superior grip no matter the surface and 2 mm of DNA LOFT v3 midsole cushioning added for extra bounce. So not only is your Glycerin Stealthfit 21 an ultra-comfortable fit but is working hard to protect the planet on whatever route or terrain you decide to take it on.