A pulse oximeter sensor is provided in which the wrap which encloses and secures the light source and detector to the body includes a sheet of metallized material. The metallized material reflects body heat back to the body and provides opacity to interfering ambient light. The wrap may be formed in a "T" shape, with the light sensor and detector aligned with the stem of the "T", or in a disposable elongated configuration with the light sensor and detector longitudinally aligned with the wrap. The wrap is secured during use through either adhesive means or by the use of hook and loop fabric patches.