When ordering silicone foam sheet, buyers often start with thickness, color and temperature resistance. Cell structure can receive less attention, even though it affects how the material handles air, moisture and compression.

A sheet used to cushion a machine component may need to behave differently from a gasket fitted around an outdoor enclosure. Both can be made from silicone foam, but choosing the same material for both jobs may lead to disappointing results.

Understanding the difference between closed cell and open cell silicone foam helps narrow down the options before requesting samples.

What Is the Difference Between Closed Cell and Open Cell Silicone Foam?

The difference lies in the small pockets formed inside the material.

In closed cell silicone foam, most cells are enclosed by walls that separate them from neighboring cells. This structure limits the paths through which air and water can travel.

In open cell silicone foam, the cells are interconnected. Air can move through the structure more readily when the material is uncompressed, which can be useful where breathability or airflow is needed.

Commercial materials do not always fall neatly into two categories. Some grades have a mixed or modified cell structure. For that reason, the description "silicone foam" alone is not enough to establish suitability. Ask for the specific grade and its technical data.

Closed Cell vs Open Cell Silicone Foam at a Glance

Neither structure guarantees a particular softness, service temperature or working life. Those properties must be checked for the individual material.

When Closed Cell Silicone Foam Is a Suitable Choice

Closed cell silicone foam is often considered for seals exposed to dust, splashes or outdoor conditions. Its structure makes it a practical starting point for equipment covers, access panels and enclosure gaskets.

However, a closed cell sheet does not automatically create a waterproof assembly. Water may still enter through a poorly joined corner, an uneven flange or a section that receives too little compression.

Consider a gasket fitted around a long metal cover. If the cover bends between fasteners, the gasket may compress firmly near the bolts while remaining loose elsewhere. Changing the foam alone may not solve the problem; the cover stiffness, fastener spacing or gasket thickness may also need adjustment.

Where an enclosure must meet a particular ingress protection requirement, test the complete assembly with the intended gasket installed.

When Open Cell Silicone Foam Makes More Sense

Open cell silicone foam is worth considering when air needs to move through a pad or escape as the material compresses. It can suit cushioning components where a solid moisture barrier is unnecessary.

For example, a pad supporting a component inside a protected housing may need to accommodate movement without applying excessive force. In that situation, compression behavior and recovery may matter more than resistance to water passage.

Open cell material should not be ruled out of every sealing application, either. Certain engineered grades can form effective seals when compressed to the appropriate level. Their suitability depends on the material, gasket width, compression and operating conditions.

The useful question is whether the selected grade performs the required job in the finished assembly.

Softness and Density Do Not Tell the Whole Story

Squeezing a sample by hand gives a quick impression of softness, but it is difficult to judge how a full gasket will behave from that alone.

A wide gasket can require considerable closing force, even when the material feels soft. This matters on lightweight doors, plastic covers and assemblies with small latches.

Ask for compression force deflection data, which describes the force needed to compress the material by a stated amount. Compare results measured under equivalent conditions.

Density is useful for identifying and comparing grades, but it should not replace compression data. Two sheets with similar density can have different force and recovery characteristics.

Check How the Material Recovers

A foam gasket may remain compressed for months before a cover is opened. Once released, it needs enough recovery to maintain contact when the equipment is closed again.

Compression set data helps assess the permanent deformation left after compression under specified test conditions. The test temperature, duration and recovery period all matter.

For equipment that heats up during operation, room-temperature results provide only part of the picture. Request data relevant to the expected conditions and include heating cycles in sample testing.

Do not assume that either open cell or closed cell silicone foam will always recover better. Formulation and grade selection are important in both cases.

Does Cell Structure Affect Heat Resistance?

Cell structure alone does not determine the temperature rating of silicone foam sheet. The silicone formulation and the conditions of use also influence performance.

Check the continuous operating temperature separately from any short-term peak rating. Then consider how heat affects compression recovery, dimensions and the adhesive backing, if one is used.

A gasket exposed to dry heat may behave differently from one exposed to steam, hot cleaning fluids or oil. Give the supplier details of these exposures rather than relying on a general description such as "high-temperature use."

For more on these factors, read our guide to choosing silicone foam sheet for high-temperature sealing.

How to Compare Samples Before Ordering

Test samples at the thickness and compression intended for production. If possible, use the final gasket shape so the trial includes corners, narrow sections and joints.

For a sealing application, check leakage under the expected conditions. For a breathable pad, check airflow while the material is installed and compressed. A sheet that passes air freely when loose may behave quite differently inside an assembly.

After the trial, inspect the material for permanent flattening, tearing or movement. If adhesive backing is included, check its bond to the actual mounting surface after heating and cooling.

This practical comparison is more useful than selecting a material from cell structure or appearance alone.

Which One Should You Choose?

For moisture-exposed equipment seals, closed cell silicone foam is usually a sensible starting point. For breathable cushioning, open cell material may be more appropriate. Where low closing force, repeated compression or a specific leakage requirement is involved, compare the data and test suitable grades.

Eshine Rubber offers silicone foam sheets and silicone sealing strips for industrial applications. When requesting a recommendation, include your gasket dimensions, installed gap, operating temperature and exposure conditions. These details help identify suitable options for sample evaluation.