What is the difference between open cell and closed cell silicone sponge?

When I first compared open-cell and closed-cell silicone sponge under a microscope, I was surprised by how much structure affects performance. The difference is invisible to the naked eye but critical in sealing and insulation applications.

Open-cell silicone sponge has interconnected pores that absorb air and water, while closed-cell silicone sponge has sealed cells that resist moisture and compression. Each type serves distinct sealing needs.

In the rubber industry, understanding the difference between these two materials helps engineers design better gaskets, seals, and thermal barriers for specific environments.

What is open-cell silicone sponge?

Open-cell silicone sponge looks soft and breathable. I often describe it to customers as “a silicone foam that breathes.”

Open-cell silicone sponge has interconnected air pockets, which allow air and water to pass through easily, making it compressible, lightweight, and ideal for cushioning or sound absorption.

When compressed, air can escape from the pores, allowing for more flexibility and softness. However, that same openness means it’s not water-resistant, so it’s rarely used for outdoor or fluid sealing applications.

Key Characteristics of Open-Cell Silicone Sponge

Open-cell silicone sponge⁶ is used in enclosures where air flow or acoustic absorption matters more than sealing. I’ve used it for HVAC damping pads and instrument cushions where moisture exposure was minimal.

What is closed-cell silicone sponge?

Closed-cell silicone sponge⁷ is what I use when a project needs a waterproof and airtight seal. Its structure is like thousands of tiny balloons trapped inside.

Closed-cell silicone sponge has sealed cells that prevent air, water, and dust from passing through, offering superior weather resistance and mechanical strength.

Because each cell is independent, it compresses under pressure but doesn’t allow liquid penetration. This makes it ideal for outdoor sealing, high-temperature gaskets, and electrical enclosures.

Key Characteristics of Closed-Cell Silicone Sponge

At Julong Rubber, we often mold or cut closed-cell silicone sponges for battery sealing in EVs and control panels, where IP65–IP67 protection levels are required.

What are the main differences between open-cell and closed-cell silicone sponge?

Both materials are made from silicone rubber but processed differently. The cell structure determines how they behave under pressure, temperature, and exposure.

Open-cell silicone sponge allows air and moisture through, offering flexibility and softness, while closed-cell sponge blocks fluids and provides better sealing and insulation.

Comparison Table: Open-Cell vs Closed-Cell Silicone Sponge

In practice, the choice depends on what the customer needs most — flexibility or sealing. Once, a client in the HVAC industry asked for a “soft waterproof sponge.” That’s an impossible combination because open-cell softness and closed-cell waterproofing cannot coexist in the same structure. We ended up using a hybrid silicone foam with a skin layer for that case.

How to choose the right silicone sponge for your application?

Choosing between open-cell and closed-cell silicone sponge depends on environment, pressure, and performance priorities.

Use open-cell silicone sponge when you need airflow or sound absorption, and closed-cell silicone sponge when you need sealing, insulation, and weather protection.

Step-by-Step Selection Guide

If you’re designing a gasket that must meet UL94 V0, IP67, or FDA requirements, closed-cell silicone sponge is almost always the right choice. Open-cell types simply cannot pass water or fire resistance tests.

I always advise engineers to test samples at the intended compression ratio — typically 20–30% for closed-cell silicone — to ensure consistent sealing performance.

Conclusion

Open-cell silicone sponge breathes; closed-cell silicone sponge seals. Understanding their structure means designing the right solution for every environment.