What is the difference between the High Strength 2 and the High Strength 3 moldmaking rubber?

The only difference between the two rubbers is hardness. The High Strength 3 is softer and more flexible making it a better choice for one piece molds that contain deep undercuts or negative drafts. The High Strength 2 has better dimensional stability and is better suited for less undercut one-piece molds and for two-piece molds due to the stiffer nature of the cured rubber allowing it to line up better with a second half of a two-piece mold.