To help you learn the language of running shoes, we've broken them down by their three main component groups. We've also called out and explained the shoe jargon that really matter—what is energy return, really? Now let's start at the top and work down from upper to midsole to outsole.
Elements of the Upper
The upper covers your foot to ensure a snug, secure fit, while providing stability.
▲ Upper Fabric: Usually made of engineered mesh (patterned for strength and flexibility) or knit that provides a close-to-foot, sock-like feel.
▲ Overlay: This layer, or layers (see the black and blue lines), of fabric provides structure to the upper and is often made of reflective materials for visibility. They may include the shape of the brand’s emblem. More shoes are forgoing overlays to reduce weight.
▲ Tongue: The tongue protects the top of your foot from the laces and is usually connected to the upper near your toes, though there are two variations. A gusseted tongue connects to the upper on its sides to keep debris out and conform to your foot more securely, but it’s more difficult to get on and off your foot. A burrito tongue—only connected on one side (shown)—also blocks junk, but is easier to put on and take off than the gusseted type.
▲ Toebox: Protects the toes and should provide ample room for them to splay, preventing toes from rubbing and blistering.
▲ Heel counter: A plastic or fabric piece that cradles the heel and provides side-to-side support. It can be internal or external (shown).
Shoe Jargon
Last The last is a manufacturer’s model that mimics foot shapes. There are three kinds: curved, semi-curved, and straight. Racing shoes are typically curved for arch support. Stability shoes are usually straight for motion control. The majority of shoes are semi-curved.
Heel lift Also called drop or offset, it’s the difference in height between the forefoot and heel. Most shoes are 8mm to 10mm. A zero- to 4mm-drop platform renders a more natural foot position. But most runners find a higher lift more comfortable, and some feel tightness in their tendons or muscles when changing from a higher to a lower heel lift.
Energy return The amount of bounce or spring inside the shoe after your foot lands on the ground. A higher percentage gives you a bouncier feeling; however, other factors affect a shoe’s responsiveness, dependent on the individual, including the runner’s weight, gait, and form.
Stability Tech built into a running shoe to assist runners who overpronate—meaning their feet roll too far inward during their stride.
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Composed of rubber-like foam, the midsole is the core of the shoe and provides cushioning and energy return.
Types of Foam
EVA: Ethylene vinyl acetate (both white and gray layers) has been the standard in midsole foams for its softness, flexibility, and low production cost since the 1970s. The downside is that it becomes more rigid in cold weather and compresses over mileage, losing its bounce.
PU: Compared with EVA, polyurethane is less sensitive to temperature, is more durable, and has a bouncier feel. However, PU is roughly 50 percent heavier than EVA.
TPU: Thermoplastic polyurethane is heated and reformed. Companies like Adidas and Saucony use a two-step process, making TPU beads and then fusing them to create a more durable, flexible, and bouncier foam than EVA and PU. However, TPU is still a heavier foam compared with EVA.
Pebax: Polyether block amide (the top, off-white layer) gained recognition as the highly responsive foam used in the Nike Vaporfly 4%. Pebax retains its flexibility and energy return in cold conditions and is 20 percent lighter than TPU.
When You May Need a Specialized Insole
Not every runner needs an orthotic insole (a.k.a. sockliner or insert), says Dr. Jordan D. Metzl, a New York City–based sports medicine physician. “There is no evidence that every person with a certain type of foot needs a correction.” For example, not all flat-footed runners overpronate and need extra stability. However, if persistent injuries—shin splints, stress fractures, plantar fasciitis—won’t pass, give an orthotic a test run. And don’t forget to take out the shoe’s insole first.
Best Winter Running Shoes for Traction and Warmth
A heel stabilizer attached to the bottom of the footbed provides support and minimizes stress on your feet during runs.
$60 | Amazon.com
Superfeet Run Pain Relief
Designed with ultramarathoner Dean Karnazes. Add heat to mold this cork-based footbed for a custom fit.
$59 | Amazon.com
Powerstep Pinnacle
Alleviates soreness from plantar fasciitis, metatarsal pain, and other foot conditions, while also providing extra cushioning.
$34 | Amazon.com
Elements of the Outsole
The outsole is the bottom of the shoe, usually made of a solid rubber or blown (air-injected) rubber, or a combination of the two. Solid rubber is more durable, whereas blown rubber—usually located in the forefoot—is more flexible and adds to the cushioning of the shoe. Depending on whether the shoe is meant for the road or trail, the outsole will either be highly segmented (a flatter tread with flex grooves) for smoother transitions on pavement, or have a more aggressive lug pattern for grip on rugged terrain.
▲ Footbridge: Also called a shank, it’s located between the heel and forefoot. It provides stability by reducing twisting.
▲ Beveled heel: A heel that’s rounded, or angled, in the back to lessen heel impact and allow you to land smoothly.
▲ Rock plate: Made of plastic typically, these protective pieces (that dark gray layer) are placed between some trail shoes’ midsole and outsole for extra defense on rocky, rooty trails.
▲ Decoupled heel: Why We Took Scissors to $330 Running Shoes.
Stability Technologies
▲ Medial post: A wedge of firm foam located below the ankle bone, in the shoe’s midsole. It’s made out of a denser material, usually EVA. The post changes the distribution of force underneath your foot as you run, reducing the stress on your ankle and causing your foot to roll inward less.
▲ Guide rails: Plates located on the sides of the shoe, inside the midsole. The guide rails couple the heel’s rotation with the knee’s (meaning the ankle’s and knee’s rotation sync with each other), thus providing support and making the runner more efficient. Brooks recently introduced guide rails to several models, including the Adrenaline GTS 19 (see our review on page 45).
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Amanda is a test editor at Runner’s World who has run the Boston Marathon every year since 2013; she's a former professional baker with a master’s in gastronomy and she carb-loads on snickerdoodles.
