Question: I am developing a new silicone part design which requires two different hardness levels on a single silicone part. Is there any kind of restriction and/or special requirement to over-mold a lower level of hardness silicone over another one?

Answer: There is no standard requirement for molding one silicone to another but points to consider: The softer silicones deflect more easily risking increased variance between parts and/or part failure. Silicone to silicone bonding in same series materials is often easier to predict than materials in different series or from different manufacturers. Two major considerations are holding and shutoff. The first shot part needs to be located and held in a mold while the over molding is done. Shutoff offs control the transition line between the two materials and directly relate to the geometry of the final part and all its components.