Silpak, Inc

How To/FAQ

Selecting Mold Material

The process of selecting a Moldmaking System can seem a difficult undertaking, at first, but understanding basic concepts and answering some fundamental questions will improve the process. There are two types of molds—Rigid and Flexible—each with its own set of inherent advantages and disadvantages. We will focus on the later—Flexible Molds— because of their simplicity, ease of use, and the ability to generate highly detailed and complex patterns with a flexible rubber compound. It should be said that a Flexible Rubber Mold, and not the converse, can make any Rigid Mold. Also, Rigid Molds are more difficult an undertaking even for an experienced professional; therefore, Flexible Molds can reproduce detailed and complex forms without much difficulty.

Which mold material is best to use depends on several factors:

1. What is the final product to be made of?
2. Is the pattern (original) soft, fragile or rigid?
3. Is there a lot of detail or undercuts on the pattern?
4. Is the mold to be made in one, two or more parts?
5. Brushed On or Poured?
6. Will it need a Mother-Mold for support?

General Rule:

Flexible Mold Materials (Silicone, Latex, and Urethane RTV) are used for producing hard parts or parts that have negative draft (undercut). Rigid Mold Materials (Plaster, Epoxy, Fiberglass) are used to produce soft and flexible parts or rigid parts that have good draft (no undercuts).

Silpak, Inc. supplies several varieties of Moldmaking rubbers, each system with its unique physical characteristics (i.e., Hardness, Elongation, Tear Strength…), processing, and casting application. All systems will reproduce virtually any surface or shape, with precise detail, providing the user with a flexible, durable, and reusable mold that can produce multiple castings. Review Table below when selecting a moldmaking rubber system:

There are two basic Mold Methods for applying these materials: Brush-On or Pour-On. The Brush-On technique is the most economical since it reduces the amount of moldmaking rubber used, although it is more labor and time intensive and is used primarily for large parts. On the other hand, the Pour On technique is the most widely employed because of how quickly and easily molds are fabricated.