An article of footwear with an insert system is disclosed. The insert system can include an insert that may be introduced to a side portion of the upper. The insert is configured to adjust properties of a side portion of an upper. The insert system can include a lateral insert configured to be inserted into an upper and associated with an inner surface of the lateral side portion. The system can also include a medial insert configured to be inserted into the upper and associated with an inner surface of the medial side portion.