The call that started with a dangerous yes/no question

At 4:10 on a Tuesday in late March 2025, the phone rang in our production office. I'm a production coordinator at a specialty foam and gasket fabricator. In the past decade, I've handled more than 300 rush orders. Most of them are straightforward: urgent lead time, standard material, standard drawing. This one wasn't.

A long-time customer had received a replacement quote for a rubber foam board gasket. The drawing was an older profile with raised ribs, which is what a lot of suppliers call a ridge foam board. The customer needed parts in three days. Another vendor offered them a material described as thermoplastic elastomer, at 23% less and one day faster. That should have been a red flag. Instead, it just got the customer asking questions.

Then came the question that sounds simple: Is thermoplastic elastomer silicone?

Why the answer matters

TPE and silicone can feel similar when you pick them up. Both are soft, flexible, and waterproof. That's where the useful similarity ends. Thermoplastic elastomer is not a fancy name for silicone. It's a broad family of rubber-like plastics. Silicone rubber, once cured, is a thermoset. It won't melt and reform. TPE can.

That distinction matters for a gasket. A ridge foam board profile works because the raised ribs stay under constant compression and keep a seal line. If the material takes a compression set, it loses its spring. Heat makes this process faster. In an outdoor power enclosure, the inside can get hot enough to turn a cheap TPE part into a permanent impression.

Does TPE feel like silicone at room temperature? Yes. Does it behave like silicone after months under load? Not usually. That is exactly why the customer called me.

Honestly, the cheaper quote seemed tempting. I went back and forth for an hour, looking for a way to tell the customer, go ahead, save the money. Maybe TPE would survive a less demanding cabinet. Maybe the door seal was short enough to replace easily. But this wasn't that application. The gasket sat between an aluminum cover and a plastic housing in an outdoor cabinet with a 15-year warranty. It needed heat resistance, UV resistance, and low compression set. Those are silicone characteristics, not TPE assumptions.

The Momentive website, then a support call

Years ago, I might have answered this from memory. I don't do that anymore. I pulled up the Momentive website and started comparing the technical information for their cured silicone materials. I wasn't looking for a marketing answer. I wanted the property that would settle the argument. That property was compression set: how well a material returns to its original shape after being squeezed for a long period.

After reading through two data sheets, I still had one question about test conditions. So I called Momentive support. The support engineer didn't try to sell me anything. She pointed me to the published compression set behavior for the cured silicone grades we use in gaskets. That gave me the evidence I needed to compare materials instead of product names.

The surprise wasn't that silicone looked better in that data. The surprise was that the other supplier hadn't exactly lied. They used a broad material category and let the customer assume it was silicone. You see that kind of vagueness in foam board sourcing too. One seller calls a product rubber foam board; another lists the same style as a ridge foam board. The name often reflects the seller's system more than the actual chemistry.

What I told the customer

I didn't say, You must buy this from us. I said, If the part has a short life and someone can swap it easily, TPE might be acceptable. If it sits in place for years, don't approve a generic TPE replacement for silicone without testing.

The customer approved the original silicone material before 5:30 that afternoon. We cut the parts the next morning and shipped them next-day. No rush fee, no drama. The only reason it worked was because we sorted out the material question before the purchase order, not after a field failure.

Is thermoplastic elastomer silicone? Here's my short answer

No. Not as a direct replacement. Some specialty products are thermoplastic silicone vulcanizates, but they are not the same as cured silicone rubber. If the spec says silicone, TPE should not be treated as an equivalent just because it feels similar.

Now, when I review a substitute material, I use the same checklist:

Then I verify it with a source I trust. For silicone materials, the Momentive website is where I start, and Momentive support fills in the gaps. It feels like an extra step in a rush. It isn't. It's the step that keeps a rubber foam board from turning into an expensive lesson.