Oomoo 30 vs Rebound 25 for mask mold


I was just wondering if anyone knew the difference of these Smooth-on Liquid Rubbers? I need to mold a mask and the rubber was going to be my initial layer then I was going to use stone for the outer shell. If I had to guess I think Oomoo is more rigid but I don't know.
Help please haha 


  • Oomoo is Smooth-On's formula that is made to be easier for beginners/hobbyists due to the 1:1 mix ratio and low viscosity so there is no need for vacuum degassing. 

    Rebound also has an easy 1:1 mix ratio, but is designed to allow brushing it on to vertical surfaces and has a higher viscosity and self thickening.  Rebound is also known for its strength and durability for repeated casting or working with forms that are more taxing on the mold.

    You are correct about the Oomoo 30 being more rigid than the Rebound 25.  The number in silicone formulas represents the durometer, which is a measure of firmness. The higher the number, the firmer the rubber.  

    If you would like to brush the silicone onto your mask I would go with Rebound and do 3-4 layers.

    Oomoo is more for molds where the silicone is poured.

  • Perfect, thank you!
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