A tear of the Anterior Cruciate Ligament (ACL) is a severe knee injury that requires up to a year of rehabilitation. Patients sustaining an ACL injury perform rehabilitation exercises mostly at home unsupervised. Orthopedists meet patients at time intervals as long as three months and lack quantitative ways to measure and keep track of the rehabilitation progress of each patient during these intervals. We present KneeHapp Textile, a smart bandage to support and keep track of the rehabilitation progress after an ACL injury. KneeHapp Textile is used by patients to obtain feedback about the quality of their exercising and by doctors to gain information about the rehabilitation progress of their patients. In this paper, we describe in detail how we constructed KneeHapp using smart textile technologies and provide insight into its software.