The Brooks Glycerin 21 Running Shoes combine super-soft cushioning and supreme comfort. These shoes are equipped with a new, engineered warp knit upper that is breathable and allows for a flexible, accommodating fit while staying soft against your foot. Their new RoadTack rubber includes recycled silica and is both lightweight and durable. They feature an additional 2 mm of DNA LOFT v3 midsole for a plush ride. Each pair are made with recycled materials equivalent to 5 plastic water bottles.