THI-VEX is made especially for thickening Smooth-On silicones for vertical surface application (making brush-on molds). Different viscosities can be attained by varying the amount of THI-VEX. THI-VEX is added as a percentage of Part A and must be thoroughly mixed with Parts A and B. THI-VEX will not work with Mold Max 40 or Mold Max 60 silicones.