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Check out our shoe-lingo decoder so you won't have to rely on the sales guy (or gal) to get a Cinderella fit from your new sneakers.
Also called a sock liner, the insole is a removable foam insert that sits under -- and often conforms to the shape of -- your foot to help the shoe fit better. Many manufacturers also sandwich extra devices (with proprietary technologies) between the insole and midsole in the heel and forefoot areas to add cushioning and shock absorption.
Sneaker treads, or outsoles, typically come in two forms: carbon rubber (usually all black) or a combination of colorful blown rubber and black carbon rubber (like that of Mizuno's Wave Inspire 5 running shoe, shown here). "Carbon rubber is more durable and can provide more traction, while blown rubber is softer and lighter for more flexibility and less weight in your stride," says Garrett Sheehan, a customer experience coach at Road Runner Sports in San Diego. Trail-shoe outsoles are almost always carbon rubber, and the deeper their lugs, the better they are for rocky terrain.
This layer is typically made of foam, which gives the shoe its cushioning and support system. (Manufacturers may also add other patented materials, such as plastic inserts, within.) "The more gray-colored material, or dual-density foam, you see by the arch, the more stability the shoe usually offers," Sheehan says. If there's no gray, it's probably a neutral/cushioning shoe (good for high arches); if the gray is mostly limited to under the arch, it's a stability shoe (good for runners with normal arches); if the gray wraps from the arch to around to the heel, it's a motion-control shoe (good for flat arches).
"The top part of your sneaker, aka the upper, is all about comfort and style," says Sheehan. "Look for one that allows your toes to move around freely and doesn't have seams that rub against your skin." While the upper can be made of any material, from leather to plastic, the more mesh there is, the more breathable your shoe will be.