7 FAQs About Dow Corning Silicone: Gaskets, O-Rings, Sealants & More

Over the past five years of tracking quotes and invoices for our manufacturing facility, I've fielded a lot of questions about Dow Corning silicone from colleagues, vendors, and even my own team. Half the time, it's not about the chemistry — it's about what works, what doesn't, and whether it's worth the premium. Here are the ones that come up most often.

1. What exactly is Dow Corning silicone — and is it different from 'silicone'?

Dow Corning is the brand name under which Dow produces its silicone materials. It's been around for decades, and when someone specifies 'Dow Corning silicone' on a purchase order, they're usually after a specific grade with traceable performance data. Chemically, it's still polydimethylsiloxane (or variants of it).

I've found that the difference shows up in consistency — batch to batch, year to year. For commodity applications, generic silicone works fine. But when we're building a custom silicone gasket for a piece of equipment that runs 24/7, I want a material I can trace back to a data sheet that hasn't changed unexpectedly.

2. How do I measure an O-ring size correctly? (And why do I keep getting it wrong?)

There's a reason this is one of the most-searched questions. The standard method is simple: measure the inside diameter (ID) and the cross-section (CS). But the trick — and this is the part that's easy to mess up — is that you need to measure the ID while the O-ring is resting naturally, not stretched.

Here's what I do after learning this the hard way: lay the O-ring flat on a clean surface and use calipers for the inside diameter. For the cross-section, pinch it gently — don't compress the material. For AS568 standard sizes, the numbers (like -112 or -214) reference a chart that gives you ID and CS in inches. But if you're working with non-standard sizes, you'll need to be accurate within 0.003 inches. That's not the time for a ruler. Ask me how I know.

Quick reference: Most silicone O-rings have a hardness around 70 durometer Shore A. Dow Corning's standard O-ring stock follows the same durometer ranges as industrial specs, but if your application involves food processing or medical equipment, you'll want the FDA-compliant grades.

3. What's the deal with Dow Corning 785 silicone sealant? Is it worth it?

Dow Corning 785 is a specific silicone sealant marketed for indoor applications — things like sealing around sinks, countertops, and baseboards. Its claim to fame is that it's 'kitchen and bath grade,' which essentially means it resists mildew better than general-purpose silicone.

In my experience, it's a good product, but not a miracle. Here's the honest take: if you're sealing a residential shower, it's fine. But for industrial or high-moisture environments where you need structural adhesion + sealant performance, you might be better served by a product specifically rated for commercial sanitation. The price premium for 785 over a standard silicone caulk is around 30-40%, depending on where you buy. I've paid it when the spec demanded it. I've also swapped it for a mid-range GE silicone when the client wasn't particular and saved about $8 per tube.

4. Can I use Dow Corning silicone to make a custom gasket for rubber wheel dumpsters?

This one's specific, but it comes up. The short answer: yes, but probably not the silicone you're thinking of.

Dumpster wheels take a beating — constant contact with asphalt, concrete, debris, and the occasional puddle of who-knows-what. A standard 40-60 durometer silicone gasket mounted between the wheel assembly and the frame can reduce vibration and seal out moisture. But you'll want a high-durometer silicone (70+ Shore A) and ideally a glass-filled or fiber-reinforced grade to handle the abrasion.

I've seen this application work well in food service dumpsters where sanitation matters. But for heavy construction debris, the gasket will degrade faster than a polyurethane or rubber alternative. Know your operating conditions.

This worked for us, but our situation was a specific customer request for odor-sealing gaskets on a commercial kitchen dumpster. Your mileage may vary if you're dealing with heavy debris with sharp edges.

5. When should I not choose silicone over rubber or TPU?

This is the question most vendors don't want you to ask. I'm going to give you the honest answer because it's saved me money twice.

Silicone is great for: high-temperature resistance (up to 500°F with specialty grades), low-temperature flexibility (down to -100°F), and electrical insulation. It's also inherently non-stick and resists UV degradation.

But silicone is not great for:

- High-frequency dynamic applications (like reciprocating seals with rapid cycling) — it can have higher friction than TPU or NBR rubber.
- Extreme tear resistance — polyurethane beats it handily in tensile tear strength.
- Cost-sensitive, low-performance applications — why pay 2x for silicone when EPDM or nitrile will do the job?

I audited our 2023 spending on sealing materials across five different product lines. For purely static applications (like face seals on flanges), silicone saved us about $4,200 annually versus using TPU. But for dynamic applications where we had frequent cycling, the silicone seals failed about 30% faster, and the replacement cost ate up any savings.

6. Is the Dow Corning logo itself a sign of quality, or is it just branding?

The logo is branding. But underneath that branding is a quality management system that's been around since 1943. I tell vendors this: if I see a 'Dow Corning' spec on a material data sheet, I know I can find the technical documentation. If I see 'generic silicone,' I'm calling the manufacturer to ask for their test procedures.

Here's the difference in practical terms: for one of our projects, we needed an O-ring kit for a valve assembly. We could buy a generic kit for $28 or a Dow Corning-sourced kit for $42 per unit. The generic kit used a 70A durometer silicone that was, on paper, identical. But actual measurements showed the generic O-rings had a cross-section variance of ±0.005 inches versus ±0.001 for the branded ones. That variance meant some seals leaked at 40 PSI. The branded ones held at 60 PSI. For a critical application, the extra $14 was worth avoiding a $1,200 redo when quality failed.

7. How do I spec a custom silicone gasket for a non-standard application?

This is where the rubber meets the road — literally. The process I've refined after six years of ordering custom gaskets:

Step 1: Know your durometer. For static compression gaskets, aim for 50-70 Shore A. For dynamic applications (think sliding or rotating), go higher, around 70-80.

Step 2: Know your temperature range. Dow Corning's standard silicone handles -85°F to 400°F continuous. If you need higher, ask about fluorine-containing silicones.

Step 3: Provide a 2D drawing with tolerances. I cannot stress this enough — without tolerances, the fabricator picks them, and you might get ±0.030 inches on the thickness, which is too loose for a critical seal.

Step 4: Ask for the test certificate. If the vendor can't provide a material lot number that traces to a specific batch, I don't buy from them for critical applications.

This was accurate as of my last procurement review in Q4 2024. Raw material pricing for silicone fluctuates with silicon metal costs, so verify current quotes before locking in a budget.