Women's Brooks® Glycerin 21 :: Your updated Women's Brooks Glycerin 21 is back again, designed to bring you unbeatable cushioning and support for running, walking or whatever your day brings! Now with extra goodies like the new RoadTack rubber that's environmentally friendly, with a recycled silica content. You can also rely on more durable and lightweight traction than ever before. If that wasn't enough, the additional 2mm of DNA LOFT v3 cushion delivers a super plush ride. Made with recycled materials equivalent to five plastic water bottles, you'll feel great with every step you take in your Glycerin 21.