Silicone vs. Thermoplastic: A Procurement Manager's TCO View on Dow Corning Materials

Here's the short version: if you're asking is rubber a thermoplastic, the answer for most engineered rubber—including silicone—is no. Cured silicone is a thermoset elastomer. Thermoplastic insulators exist, but they're not a substitute for a silicone housing on an automotive sensor or a high-voltage insulator. And if you need a clear plastic box for packaging, don't use silicone at all—use PET or acrylic. The material decision comes down to function, and the cost decision—or rather, the decision that keeps me up at night—comes down to total cost of ownership, not price per kilogram.

I manage purchasing for a 90-person industrial components company. I've controlled a materials budget of about $1.2 million a year for 6 years. When I audit our orders, I keep finding the same pattern: per-unit price is the least reliable number on a material quotation. In Q2 2024 alone, comparing quotes across 4 suppliers for the same silicone seal, I saw pricing spread of 38% from low to high. After factoring in lead times, failure rates, and rework, the “cheap” quote was the most expensive one in the lot.

Why I'm the wrong person to ask about material science—and the right person for cost

I'm not a chemist. I don't formulate compounds. What I do is track every invoice, every rejection, every field failure, and every rework ticket. Over the past 6 years, that track record has made me skeptical of two things: suppliers who say “silicone is silicone,” and buyers who pick material based on the lowest quote.

When I started in this role, I believed the conventional wisdom: buy by specification, choose the cheapest compliant option. In practice, I found that compliance on paper doesn't predict performance in the real world. The seal that passed the bench test failed under heat cycling. The plastic clip that looked identical broke in February. My procurement policy now requires quotes from at least 3 vendors, but more importantly, it requires asking every vendor: “Show me where this material failed.” It sounds like an odd question. I've never had a supplier refuse to answer, and the answers have saved me more money than any discount.

What “dow corning silicone automotive” actually costs

Under the hood, silicone earns its keep. The search phrase “dow corning silicone automotive” usually comes up around gaskets, connectors, and wire insulation. Those parts have to tolerate engine heat, oil, vibration, and water. A silicone elastomer can handle that. Many thermoplastics cannot, or at least not for the same service life.

Let me give you a real comparison from our 2024 parts audit. We tested two sources of a sensor gasket. Supplier A quoted $2.10 per unit for a Dow Corning silicone compound. Supplier B quoted $1.80 for a tin-catalyzed silicone “just as good.” The initial quote made B look 14% cheaper. But B's parts failed our thermal shock test in the first run. Re-testing, scrapping the bad batch, and rushing the correct material cost us about $1,200. That's $0.80 per unit when divided across the order—more than the entire per-unit difference. The “cheap” option was 38% more expensive when the total cost was captured.

In 2022, we made a different decision. We qualified a lower-cost thermoplastic for an interior part—not exposed to engine heat. It worked fine. The same material would not have worked under the hood. That's the nuance: silicone is not always the answer, but the answer you get from a cost spreadsheet depends on what you're measuring.

The TCO filter I use

I don't reject a thermoplastic just because silicone is a better seal. I ask four questions:

• What temperature does the part actually see?
• What is the expected service life in years?
• If it fails, what will it cost to replace?
• Does the material have third-party test data or only the supplier's brochure?

For a non-structural cover, a clear plastic box might be perfectly sufficient. For a brake sensor, I'll pay for silicone.

When a clear plastic box wins

Here's where I sound like the opposite of a silicone salesperson: if you search for a clear plastic box for packaging, do not buy silicone. A clear PET or acrylic box costs a fraction of a silicone container, offers clearer transparency, and is the correct engineering choice. I once had a vendor try to upsell me on silicone for a transparent retail display. I thanked them, bought the PET version, and never called them for a quote again.

The vendor who actually won my business said: “This is a packaging application. Silicone is not our recommendation here—go with PET. We'd be glad to quote you when you need high-temp seals.” That honesty earned them four orders in the following year. That's the expertise boundary I respect: a specialist who knows where they don't fit is a specialist I trust.

Is rubber a thermoplastic? A purchasing answer

The exact question comes up more than you'd think: is rubber a thermoplastic? In everyday language, “rubber” includes both thermoset rubber and thermoplastic elastomers (TPE). But if you mean the rubber that makes an automotive gasket, it's almost always a thermoset: it cures into a crosslinked network that does not melt again.

Silicone rubber is in that category. Once cured, it can't be re-melted and re-processed like a thermoplastic. According to ASTM D2000, rubber materials are classified by heat and oil resistance, not by a vendor's nickname for them. That's why “dow corning silicone” parts are not the same as thermoplastic parts from a molding or recycling standpoint. They're different material classes with different process economics.

Thermoplastic insulators are a different story. You'll see them in lower-voltage and indoor applications where recyclability and processing speed are advantages. But for high-voltage outdoor insulators, thermoset silicone or EPDM is often specified because they resist tracking, erosion, and UV aging better. I'm not a dielectric specialist, so I don't make blanket pronouncements. My point is narrower: “thermoplastic” is not a synonym for “cheaper and just as good.” It's a material class with its own boundaries.

The unglamorous lesson: ask for failure data, not promises

I only became serious about failure data after getting burned. In 2020, I approved a switch to a lower-cost plastic for a connector housing because the spec sheet looked right. We saved $1,700 on the initial buy. Eight months later, we got complaints about cracked housings on outdoor equipment. The replacement order, plus the labor to swap the parts in the field, cost us about $4,800. The “budget” choice ended up being a $3,100 mistake. I still check that material approval every time I look at the budget—it's a reminder that a material spec is a promise, and not all promises are equal.

Since then, I've built a simple cost calculator in our procurement spreadsheet. Whenever we choose between a silicone and a thermoplastic, I enter the unit price, expected failure rate, rework cost, and field replacement cost. It's not sophisticated math. It's just the math the initial quote never shows.

A short note on “dow corning silicone breast implants”

One of the search terms that might land on this article is “dow corning silicone breast implants.” I don't buy medical devices, and I'm not going to pretend to have expertise there. That is exactly the point. Dow Corning makes medical-grade silicones, but an implantable grade and an automotive grade are not interchangeable. They share a chemistry family, not a specification. A vendor who says “we don't do medical devices—talk to a specialty manufacturer” is more credible than one who says “silicone is silicone, use this one.”

The same logic applies to thermoplastic insulators, food-grade seals, and clear plastic boxes. The material class is a starting point, not the final answer. You need the specific grade, the specific test data, and a supplier who will tell you when you're asking for the wrong thing. My rule: if a supplier is genuinely better elsewhere, I want to know. It beats finding out after the parts fail.

What I'd still tell a younger buyer

None of this means silicone is always the right answer. If your part sits in a conditioned office, a clear plastic box made of PET is better, cheaper, and easier to recycle. If you need a one-time prototype, a 3D-printed thermoplastic will get you there faster. If you're in the medical implant field, ignore my procurement logic and listen to your regulatory team.

The best material is the one that passes the tests and minimizes total cost over the part's life. That's a boring conclusion, but after six years of audits, boring budgets are the ones I trust.