The outsole is the treaded layer glued to the bottom of the midsole. It resists wear, provides traction, and absorbs shock. The outsole is usually blown rubber, hard carbon rubber, or a combination. Blown rubber is the lightest, but not as durable as carbon. Stud or waffle outsoles are good for running on dirt or grass because they improve traction and stability.
Ripple soles are better for running on asphalt or cement surfaces.
The heel counter is the inflexible material surrounding the heel. It must be rigid and durable to support and stabilize the heel. Because the internal heel counter material is thin and tends to lose its stiffness, an external counter is usually placed between the midsole and base of the heel counter. A wedge, which adds height to the heel, enhances the shoe's ability to absorb shock and reduces strains. While this can ease problems like Achilles tendinitis, a shoe with a higher heel may feel less stable.