Vacuum Degassing vs. Self-Degassing LSR in Mold Making
When I work with mold-making liquid silicone rubber (LSR), one of the most common questions I hear is whether vacuum degassing is really necessary. Some suppliers promote "self-degassing" silicone as a way to simplify the process, while others strongly recommend vacuum degassing for professional results. The truth is that both approaches have their place. The key is understanding how they differ and when each one makes sense.
What Is Vacuum Degassing in Silicone Mold Making?
Vacuum degassing is a process where I place mixed liquid silicone rubber into a vacuum chamber to remove trapped air bubbles before pouring. When the pressure drops, air expands and escapes from the silicone. After a few minutes, the silicone collapses back down into a bubble-free liquid.
I typically use vacuum degassing when:
The mold has fine details
The silicone has medium to high viscosity
Surface quality matters
I need consistent, repeatable results
Vacuum degassing adds an extra step, but it significantly reduces the risk of voids and surface defects.
What Is Self-Degassing Liquid Silicone Rubber?
Self-degassing LSR refers to silicone formulations designed with very low viscosity and good air-release characteristics. These materials allow air bubbles to rise and escape naturally after mixing, without the need for a vacuum chamber.
In practice, I simply mix the silicone slowly, let it sit briefly, and then pour it in a thin stream. Gravity and flow help eliminate most bubbles.
Self-degassing silicone works best when:
The mold geometry is simple
The silicone viscosity is very low
Production speed matters
Vacuum equipment is unavailable
Key Differences Between Vacuum Degassing and Self-Degassing
The biggest difference lies in process control. Vacuum degassing gives me predictable results across different mold designs. Self-degassing relies more on formulation quality, mixing technique, and pouring skill.
From my experience:
Vacuum degassing produces cleaner surfaces and sharper details
Self-degassing saves time and reduces equipment costs
Complex molds benefit more from vacuum degassing
Simple molds work well with self-degassing silicone
Impact on Mold Quality and Detail
When I make molds with deep undercuts, thin walls, or fine textures, trapped air becomes a serious problem. Even small bubbles can compromise mold accuracy or tear strength. In these cases, vacuum degassing gives me peace of mind.
For flat molds, open-face molds, or low-detail parts, self-degassing silicone often performs well enough. I still pay attention to slow mixing and controlled pouring to minimize air introduction.
Production Efficiency and Cost Considerations
Self-degassing LSR clearly wins on convenience. I do not need a vacuum pump, chamber, or additional setup time. This approach suits small workshops, prototyping, and on-site mold making.
Vacuum degassing increases upfront investment but reduces scrap rates in demanding applications. In professional mold production, the added consistency often justifies the cost.