Over the years working in industrial components manufacturing, I've frequently received questions from customers: "Isn't a foam silicone gasket just a soft ring? You can simply buy any one."
This is not the case. Selecting incorrect materials, using inappropriate density values, or neglecting compression ratios can lead to minor issues such as air or water leakage, or severe consequences like equipment damage or even safety incidents. Today, we present 3 real-world examples to help you avoid the "hidden pitfalls" associated with foam silicone rings.
Under high-temperature conditions, ordinary foam pads deteriorate into powder within three months.
A manufacturer of new energy battery packs reported that the foam sealing rings they used lasted less than one quarter before surface cracks appeared, and they would break upon compression when disassembled. The ambient temperature was not extreme (typically around 80°C over extended periods). What could be the reason for this phenomenon?
Analysis revealed that the purchased components were standard EPDM foam rings, which have a long-term temperature resistance limit of only around 120°C, whereas silicone foam rings can withstand up to 250°C. Although 80°C does not exceed EPDM's maximum tolerance, localized hot spots within the battery pack, combined with environmental factors such as ozone and humidity, accelerate EPDM aging. In contrast, silicone foam rings, with their Si-O-Si backbone structure, exhibit superior resistance to ozone, ultraviolet radiation, and high-temperature aging, extending their service life by 3–5 times under identical operating conditions.
Advice: For devices exposed to temperatures above 60°C or outdoor environments for extended periods, foam silicone rings should be preferred over conventional rubber foam.
Case 2: Seal failure is not due to improper sealing but rather to an incorrect calculation of compression ratio.
An outdoor LED display manufacturer requires IP68 waterproof certification. They employed closed-cell foam silicone rings with a hardness of 40 Shore OO and a thickness of 5 mm. During post-installation rain exposure testing, water penetrated some products. Disassembly revealed that the sealing rings were severely compressed, with certain sections even fractured.
The issue lies in the compression ratio design. The recommended compression range for foam silicone rings is typically between 15% and 30% (for closed-cell structures). However, to achieve a perfect seal, the groove depth was designed at only 3.8 mm, resulting in an actual compression ratio of (5 – 3.8)/5 = 24%, which appears within the specified range. Yet foam materials exhibit stress relaxation; prolonged compression reduces their rebound force, combined with uneven local stress distribution during installation, ultimately leading to sealing failure.
Subsequently, we recommended adjusting the groove depth to 4.2 mm (with a compression ratio of 16%) and adding a limiting structure, thereby resolving the issue. Additionally, open-cell foam silicone rings can achieve higher compression ratios (30–50%), but closed-cell variants are typically used in applications requiring stringent waterproofing performance.
Advice: The selection of expanded silicone rings should not be based solely on thickness; a comprehensive evaluation incorporating groove depth, hardness, and permanent compression deformation rate is required. It is recommended to obtain compression force-deformation curve data from the manufacturer.
Case 3: Although appearing identical as black foam rings, their flame retardant performance varies significantly.
A charging station customer required UL94 V-0 flame retardancy certification. They purchased a batch of black foam silicone rings from the market, which could be extinguished even during a lighter test. However, inspection revealed that in the vertical combustion test, the burning droplets from the samples ignited the underlying absorbent cotton-a behavior prohibited under V-0 standards.
Why? Because conventional foam silicone contains only a small amount of flame retardants or utilizes halogen-based flame retardants (which are environmentally harmful and prone to leaching at high temperatures). A truly V-0 certified foam silicone ring requires a halogen-free flame retardant system, uniform cell structure, and no dripping of products during combustion.
We offer customers a version certified to UL94 V-0 standards, compliant with RoHS and REACH regulations, and having passed both the needle flame test and hot wire test. Although the cost is indeed 20% higher than that of the standard version, safety redundancy is essential for high-power devices such as charging stations.
Advice: If the product involves electrical safety (new energy, household appliances, rail transit), it is imperative to obtain a flame retardancy certification report rather than relying solely on superficial evidence.
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