In most cases, silicone molds are preferred for vacuum casting due to their flexibility, ease of use, and excellent detail reproduction. However, when you’re casting silicone parts, the mold material typically changes. Understandably, you’re concerned, as stickiness might result from using silicone molds in some situations during the curing process.

ABS plastic molds are often used for silicone casting. ABS can be an alternative to the more commonly used silicone, as it helps the silicone adhere less closely to it, simplifying demolding.  It is a non-reactive material and does not interfere with the curing process. So, while silicone is the standard for most molds in casting, ABS would be the better choice for casting silicone parts.

Just wanted to add that when you’re using the vacuum casting method, the use of ABM molds will make your work much easier, as they can easily be machined and are durable enough for repeated use. It’s important, however, to ensure proper mold preparation, usually through the application of a release agent, so that parts can easily be demolded without being damaged.