There's No 'Best' Material—Only The Best Fit For Your Specific Conditions

If you're looking for a simple answer on whether to use silicone or rubber for your next batch of seals, gaskets, or O-rings, I have to stop you right there. In my 4 years as a quality compliance manager, I've reviewed roughly 1,200 unique parts—everything from small-diameter O-rings for hydraulic manifolds to large-format silicone foam seals for HVAC enclosures. And the one thing I can tell you for sure is that there's no universal winner.

The material that works perfectly for one application can fail spectacularly in another. I've seen it happen. What I can give you is a decision framework based on three common industrial scenarios. Figure out which one you're in, and the path becomes much clearer.

Scenario A: High-Temperature Environments (Continuous Exposure Above 200°C / 392°F)

This is the scenario where silicone is your obvious—and often only—choice. Standard EPDM or nitrile rubber will start to degrade and harden. But even here, you have to specify the right grade of silicone.

In Q1 2024, I reviewed a batch of 5,000 silicone gaskets intended for a curing oven door seal. The spec was for a general-purpose, 40-durometer silicone. The problem? The supplier used a standard tin-cure silicone, which maxes out around 230°C continuous. The actual application was a 250°C cycle with a 10-minute soak every hour. After 90 days, the gaskets had become brittle and were cracking at the corners.

What I'd suggest instead: For anything above 200°C, specify a peroxide-cured or platinum-cured silicone. They hold their integrity longer. Also, request a thermal gravimetric analysis (TGA) report to confirm the filler content. In that failed batch, we found the filler ratio was too high, which accelerated the breakdown.

For this scenario, you're basically looking at silicone. But don't just write "silicone" on your spec sheet—be specific.

Scenario B: Dynamic Sealing & Abrasion Resistance (Moving Parts & Constant Contact)

Here's where conventional wisdom gets flipped on its head. Most people assume silicone is a premium material, so it must be better for everything. Not even close. For dynamic seals—like a rotating shaft seal or a reciprocating piston seal—silicone is actually a poor choice. It has lousy tear resistance and poor abrasion characteristics.

I ran a blind test with our maintenance team a few years back: same-sized V-ring seals made from 70-durometer silicone and 70-durometer polyurethane. I won't bore you with the raw data, but 8 out of 10 technicians identified the silicone seal as 'already failing' after a 48-hour test on a low-RPM shaft. The PU seal showed barely any wear. The cost difference? The PU seal was about $1.10 per piece vs. $0.85 for the silicone. On a run of 50,000 units, that's $12,500 for dramatically better field performance. It's a no-brainer.

The bottom line: If your application involves constant motion or friction, look at polyurethane (for excellent wear) or a high-grade NBR (nitrile) for oil resistance. Silicone is a sitting duck here. This is the most common mistake I see in part specs.

Scenario C: Extreme Low-Temperature Flexibility & Environmental Sealing (Below -40°C / -40°F)

Standard rubbers become glass-like at very low temperatures. An EPDM seal that's perfectly flexible at room temperature can become rigid and fail to seat at -50°C, leading to a leak. This is where silicone excels again. Its glass transition temperature (Tg) is inherently low—typically around -120°C for standard grades.

We source a lot of silicone foam for outdoor telecom cabinet seals. In one instance, a competitor claimed their sponge EPDM could match silicone's low-temp performance. It wasn't even close. At -40°C, the EPDM compression set was 60%—meaning it lost 60% of its ability to return to shape. The silicone foam maintained a compression set of under 15%.

But here's the catch: for truly static outdoor sealing, silicone foam is often overkill on the low-temp end if your actual winter temps only hit -30°C. A high-quality EPDM with a properly formulated low-temp recipe might save you 30-40% in material cost. The key is knowing your actual minimum temperature, not the worst-case number from a climate map. Measure it at the installation point.

How Do You Know Which Scenario You're In?

Honestly, the easiest way is to stop guessing and ask three specific questions:

  1. What is the actual, measured temperature at the seal interface? Not the ambient temperature of the machine, but the steel-to-rubber contact point. Use a thermocouple, don't guess.
  2. Is the part moving relative to what it's sealing? A static gasket is a different beast entirely from a wiper seal on a hydraulic cylinder. If motion is involved, the abrasion resistance is king.
  3. What is the chemical environment? Silicone is great for water and steam. It's terrible for concentrated oils. NBR is great for oils. EPDM is great for coolants. A common mistake is using a chemically incompatible material for a seal that will live in a specific fluid.

Take the time to match your application to the material's strengths. It's way cheaper to spend a day on specifications than to deal with a field failure that costs you a $22,000 equipment redo—which, I can tell you from experience, is exactly the cost of ignoring this step.