Silicone Rubber Cast Molding


Very basic tutorial for mixing, casting, and curing silicone rubber in molds. This technique is a starting point for silicone-based soft robotics.


Preparation time: 20 min
Process time: 1 hr


Tools and Equipments

  • Non-silicone molds
  • Kitchen scale
  • Oven (optional)


Scale Molds

First, let’s see how much silicone rubber is needed for the mold. Pour water into the molds instead of silicone rubber. Gather the water into a cup and weigh it. This value is about the same amount of silicone rubber necessary to fill the molds. When measuring the silicon rubber, we will add an extra 10-20% to this amount.


Pour Ecoflex part A into a cup. It should be half of the required amount of silicon rubber. Pour the exact same amount of Ecoflex part B into the same cup. If you have poured more than the required amount of part B, then add more part A so that they are the equal amount.


Slowly mix the silicone with a mixing stick for 1 minute. Avoid brisk mixing movements to prevent from making bubbles. Mix well while scraping the silicone from bottom and side of the cup.


The molds should be made of non-silicone material such as PP (polypropylene), PE (polyethylene), and PET (polyethylene terephthalate), otherwise the silicone mold will fuse with the casted silicone. Pour the silicone into the molds. Wipe off the overflowed silicon with a paper towel.

Rest and degas

Leave the silicon rubber for 10 minutes for degassing. For simple molds, vacuum pumps are not necessary because Ecoflex’s viscosity is not that high.


Bake in an oven at 60°C (140°F) for 20 minutes to accelerate curing. If you don’t have a oven, just wait for 4 hours at room temperature.


Take out the silicone rubber from molds. Cut off the excess silicon on the edges with scissors.


Bon Appétit! (but don’t eat)



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