Dow Corning Products FAQ: Silicone Grease, FFKM O-Rings, and Material Selection

I manage MRO (maintenance, repair, and operations) purchasing for a manufacturing plant with roughly 300 employees — about $400K in annual spend spread across 15 vendors. When I took over the role in 2021, I knew more about office supplies than industrial elastomers. Three years of trial and error later, these are the questions my colleagues ask me most, and the answers I learned the hard way.

• What's the difference between Dow Corning silicone grease and regular petroleum grease?
• Which Dow Corning products should I stock for routine maintenance?
• Can I just buy generic silicone grease instead of Dow Corning products?
• Why do FFKM o-rings cost so much more than regular o-rings?
• What's the right o-ring gland design for FFKM?
• Polystyrene vs polypropylene — which should I order?
• What's the most common mistake when buying Dow Corning products?

What's the difference between Dow Corning silicone grease and regular petroleum grease?

The short answer: silicone grease uses silicone oil instead of petroleum oil. That distinction matters more than you'd think. Petroleum-based grease can attack rubber and many plastics, causing swelling, softening, or cracking over time. Silicone grease is much more compatible with elastomer seals, which is why it's the go-to for o-rings, valves, and rubber parts.

It also handles a wider temperature range. Molykote 111, for example, is rated roughly -40°C to +204°C. But it isn't a universal lubricant — for high-load metal-on-metal applications, you probably want a heavier grease with more film strength.

From the outside, it looks like you're just paying more for the same slippery stuff. The reality is that a $15 tube of the wrong grease can cause a seal to fail in weeks. I made that mistake once: saved $30 on the wrong product, and it cost us about $700 in replacement parts and internal labor. (Which, honestly, still bothers me.)

Which Dow Corning products should I stock for routine maintenance?

I can only speak to light industrial maintenance — that's my experience base. The items I reorder most are:

• Molykote 111 Valve Sealant & Lubricant — for valves, o-rings, and rubber seals. Wide temperature range and works with most elastomers.
• Molykote 4 — a multipurpose silicone grease for plastic and rubber parts, often used as a dielectric insulator too.
• Molykote 55 O-Ring Grease — formulated specifically for rubber o-rings in pneumatic systems.

If you see "Dow Corning" labels on older stock, it's the same product line — Dow Corning integrated into Dow in 2016, and most products now carry the Molykote brand.

If you work in food processing or medical, your stock list will look different. You'll need NSF H1 or similar certifications, and I don't deal with that enough to hand out advice. The broader lesson is to standardize on a few products and keep their datasheets on file. That way, when someone asks for "silicone grease," the follow-up question — "for what application?" — answers itself.

Can I just buy generic silicone grease instead of Dow Corning products?

Sometimes, yes. If you're greasing a cart wheel or a door hinge, generic silicone grease is perfectly fine. The line I've drawn for myself: if the application involves a seal, a certification requirement, or a warranty, I buy the branded product with a published datasheet.

Here's why. Branded products come with traceable specs — exact temperature limits, compatibility data, and certifications. A generic tub might say "silicone grease" and nothing else. When my team needs to know whether a lubricant is safe for an oxygen-service fitting or a food-contact valve, the datasheet answers that. The generic tub doesn't.

It's tempting to think all silicone greases are interchangeable because they look and feel the same. They aren't. Fillers and thickeners differ between formulations, and those differences show up when the application gets demanding.

Why do FFKM o-rings cost so much more than regular o-rings?

Every time someone requests an FFKM o-ring, they flinch at the quote. FFKM (perfluoroelastomer) is essentially the result of combining rubber's elasticity with PTFE's chemical resistance. That chemistry is expensive to manufacture. A single FFKM o-ring can run $50 to $200 depending on size and grade, while an FKM (Viton) equivalent might cost $3 to $10.

The instinct is to choke and order the cheaper option. I get it. But I've also watched a standard o-ring swell and degrade inside a $10,000 assembly because the chemical exposure was more aggressive than the material could handle. The replacement cost makes the price premium look trivial.

My rule now: before ordering FFKM, I confirm the actual chemical exposure and operating temperature with the maintenance engineer. About half the time, the job genuinely requires FFKM. The other half, FKM or EPDM will do the job at a fraction of the price. That 10-minute verification is the cheapest insurance I've found.

What's the right o-ring gland design for FFKM?

Gland design is where o-ring failures really start. The gland is the groove that holds the o-ring, and if its dimensions or surface finish are wrong, the best o-ring in the world will leak.

General guidelines: for static applications, the o-ring is typically squeezed 10% to 25% of its cross-section. Dynamic applications use less — usually 5% to 15% — because friction and wear become factors. You also want a gland fill around 75% to 85%, meaning the o-ring occupies that portion of the gland volume at rest. Less and the seal can shift; more and it has no room to swell when heat or chemicals do their thing.

FFKM adds another layer of caution. It's mechanically similar to FKM but has lower elasticity at the same hardness, so tolerances matter more. I always reference SAE AS568 for standard o-ring sizes and pull gland dimensions from ISO 3601 or the seal manufacturer's design handbook. Guessing on gland dimensions is the classic way to turn a $50 seal into a $5,000 redesign.

Polystyrene vs polypropylene — which should I order?

To a non-engineer, these two names sound almost interchangeable. They aren't. Polystyrene (PS) is rigid, clear, and easy to fabricate, but it's brittle and has weak chemical resistance. It softens in the neighborhood of 100°C. Polypropylene (PP) is tougher and more flexible, resists far more chemicals, and handles higher service temperatures — its melting point is roughly 160-170°C, though continuous-service limits are lower.

My simplified rule: if the part needs clarity and stiffness, PS is usually the pick. If it faces solvents, moisture, or repeated stress, PP is the safer bet. The real answer always comes from the application requirements, not a general preference.

I once ordered polystyrene parts for a run that ended up contacting solvent. The parts crazed and cracked within weeks, and we had to redo the entire batch. I'd saved the requestor a little money on unit price and cost the department far more in replacement. Now I ask about chemical exposure before I order any plastic. I've learned not to apologize for asking that question.

What's the most common mistake when buying Dow Corning products?

Spec mismatch. Almost every problem I've run into traces back to someone ordering the right category but the wrong variant. Real examples from my files:

• Ordering "silicone grease" without checking whether the application needs NSF food-grade certification.
• Buying Molykote 4 when they needed Molykote 111. Both are silicone greases, but they're not interchangeable.
• Choosing an FFKM o-ring grade on price alone, without confirming durometer or chemical compatibility.

My checklist for every order has three items: application (what does the product touch), certification (does the industry require a rating), and temperature (what's the operating range). Five minutes of verification before I place the order beats five days of downtime after a failure. I built that checklist after my third mistake, and it's already caught two potential failures this year.