An improved article of footwear includes a sole structure and an upper. The upper is coupled to the sole structure and is configured to receive at least a portion of a human foot. The upper further includes a toebox, a medial quarter, a lateral quarter, a heel cup. The upper also includes a three dimensional auxetic structure at least partially formed within the medial quarter, lateral quarter, and heel cup of the upper. The three dimensional auxetic structure defines a primary expansion direction, a secondary expansion direction, and a tertiary expansion direction. The secondary expansion direction is transverse to the primary expansion direction. The tertiary expansion direction is normal to the plane defined by the primary expansion direction and the secondary expansion direction. Furthermore, the upper of the article of footwear is constructed via a thermoforming process.