Ta'weez carries Quranic words or names of Allah (SWT) or words of the Prophet (SAWA ) or Ahlul Bayt (AS). No doubt, theses holy words have an effect of blessing and protection. You read in Quran how the prophet Yousuf sent his shirt with his brothers to cast it on the face of his father, Prophet Ya'qoub (Jacob) who lost his eyesight, so that he will get back his eyesight. Sura 12, verse 93).
This is a very clear Quranic evidence that there is miraculous effect of certain materials because of the blessings of humble servants of Allah (SWT).
Real Ta'weez from Quran and Ahlul Bayt (AS) is something like that with different degree.