Mold and Foam General Prop Questions


New Member
I am working on a first project polyurethane and Foam.
I was told use 10 lb Foam, which makes sense, but the mold is what I am struggling with.

The mold I want for about 10 copies of the part I want, but making a second mold won't break my heart. When different sources recommend Poly 74-29 or Poly 73-20 and such I am really lost.

Can I get some advice on picking a mold material and what the numbers mean? "Poly XX-YY"
I really want to understand what I am working with and why.

Thanks guys!
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Sr Member
it looks to me like those are just 2 different kinds of silicone for molding with
the poly 74-29 is used for making concrete molds and the poly 73- 20 is a clear silicone so you can do a solid mold then use an exacto blade to cut the mold lines.

i like using "oomoo 30 silicone" from a company called smooth on.
its a 2 part silicone that you mix 1 to 1 so you don't need a digital scale to use it. and i've gotten about 50 casts out of each mold no problem.

make sure what ever you are making the mold with doesn't have sulfur in it!! sulfur messes up silicone and won't let it cure right.

hope this helped a little

and welcome to the site!
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