A heel counter, also referred to as a 'heel guard', 'moulded counter', 'heel overlay', or 'heel protector', is placed onto the rear of a shoe's upper and is usually stitched and glued onto the base material of the upper.
The purpose of a heel counter is to provide stability and protection. In the past most Adidas shoes did not require a heel counter because the material used in the upper of the shoe were inherently stable; materials like leather and suede. However, modern Adidas shoes, and especially modern Adidas running shoes, have stopped using leather and suede in their construction: to ensure that the shoe is lightweight and breathable. Lightweight materials, like canvas and mesh, improve performance because they let the foot to breath by placing holes in the weave of the fabric, and due to their light weight. The drawback is that these materials are flimsy, and due to the forces that are placed on the heel area of a shoe, can quickly lead to the foot not being held firmly, which can lead to injury. The heel counter aims to fix this issue, and is used on shoes like the Adidas Pure Boost and Adidas ZX Flux.