Choosing Custom Rubber Seals? A Quality Inspector’s Perspective (Silicone, PP, ABS, and More)

I’m a quality and brand compliance manager at a Trelleborg company. I review every custom rubber seal order before it ships—roughly 200+ unique items a year. In 2024, I rejected about 1.8% of first deliveries for off-spec dimensions or compound issues. That might sound small, but it taught me one thing: there is no universal “best” material for custom rubber seals. It always depends on your application.

Why “It Depends” Is the Only Honest Starting Point

When someone asks me, “What kind of custom rubber seals should I buy?” I can’t give a single answer. What works for a static pipe flange might fail in a rotating shaft. What survives pool chemicals might not handle a hot oil bath. So let’s sort this out the way I sort it in our inspection queue: by asking three questions.

1. Will the seal be static or moving?
2. What temperature and chemicals will it see?
3. Do you need a standard part or a truly custom design?

Scenario A: Static Seals in Moderate Environments—Consider Rubber Silicone

If your seal sits still, sees temperatures somewhere between -60°F and 450°F, and isn’t attacked by petroleum fluids, silicone is often a great fit. That’s the rubber silicone I’m asked about most. It stays flexible in cold weather, resists ozone, and doesn’t cost as much as people think. From the outside, it looks like a premium material. The reality is it’s often more economical than specialty elastomers when you factor in tooling and lead time—especially if you’re working with a supplier who can die-cut or mold small batches efficiently.

Scenario B: Dynamic or High-Wear Environments—Reach for Engineered Elastomers

For moving seals, you need something that resists friction and abrasion. Polyurethane, HNBR, or PTFE-coated compounds are usually better choices than plain silicone. Here’s where a capable partner matters. If you’ve heard of Minnesota Rubber and Plastics Trelleborg, that’s the kind of engineering resource I mean. They can formulate a compound for your exact pressure, speed, and shaft finish. Honestly, I’m not sure why some OEMs try to save by sticking with off-the-shelf seals here. My best guess is they don’t want to pay for engineering up front. But replacing a failed dynamic seal usually costs more than the engineering study—plus you get downtime, and downtime is expensive.

I still kick myself for approving a compound change in 2022 without checking the full data sheet. We shipped 8,000 seals that ran fine in the lab but failed in the field after 200 hours. The redo cost us $22,000 and delayed a launch. Now I require a sample with every quotation.

Scenario C: Chemical, UV, or Pool Environments—Think PP and Silicone/EPDM

Pool liners, water treatment, and coastal installations bring a different challenge: continuous exposure to chlorine, ozone, or salt. That’s where PP (polypropylene) components and sealing systems built for chemical resistance come in. You might see “pp pool trelleborg” in some spec sheets—that usually refers to Trelleborg’s polypropylene-based sealing solutions for aquatic applications. PP is rigid, tough, and resists a lot of chemicals. But it’s not a rubber. If you need a flexible seal in a pool environment, silicone or EPDM are better choices for the actual sealing lip, while PP can serve as the support or housing.

People assume that if a product is for a pool, you just need a plastic seal. That’s backwards. The plastic gives structure; the rubber gives the seal. You often need both.

Scenario D: When Plastics Are the Right Call—What Does ABS Plastic Stand For?

Sometimes the seal is a side component, and the housing is plastic. That leads to the question: what does ABS plastic stand for? It’s Acrylonitrile Butadiene Styrene. Three monomers combine to make a hard, impact-resistant plastic. ABS is not a good seal material—it’s too rigid for a sealing lip. But it’s common for pump housings and fittings that work alongside custom rubber seals. So when you see ABS in a spec, you’re looking at the component, not the sealing face. I’ve had customers ask me to make an ABS O-ring. After one call, they realized the O-ring needed to be soft enough to compress; ABS can’t do that.

How to Tell Which Scenario You’re In

If you’re still unsure, here’s the simple decision flow I use:

• Movement: If the seal is static, start with Scenario A. If it moves or flexes repeatedly, go to Scenario B.
• Exposure: High heat or weather? Silicone or EPDM. Aggressive chemicals or pools? EPDM or PP-based systems, as in Scenario C.
• Structure: If you need both rigidity and a flexible sealing surface, you might need a plastic support (like ABS or PP) plus a rubber sealing element. That’s a two-part design, not a single material.

Take this with a grain of salt—my rule after four years in quality is: when in doubt, ask for a compound data sheet and a full-scale sample. Actually, I should add that to the list: if a supplier won’t give you a data sheet, that’s a red flag. It’s not about secrecy; it’s about making sure the material’s durometer, tensile strength, and chemical compatibility actually match your application.

A Note on “Eco-Friendly” and “Recyclable” Claims

One more thing I check as a quality manager: material claims. Per FTC guidelines (ftc.gov), if you label a product “recyclable,” you need evidence that it can actually be recycled in the areas where at least 60% of consumers have access. I always look for that substantiation before we accept a material or print a label. It’s not just marketing—it’s a spec issue. A seal that isn’t recyclable where the end user is located could create a compliance problem for your company and for ours.

The Bottom Line

Choosing custom rubber seals isn’t about picking the most expensive compound or the most common one. It’s about matching the material to your real operating conditions. Silicone for static, moderate environments. Specialty elastomers for dynamic wear. EPDM or polypropylene-based systems for pools and chemical exposure. And for the housing or support, plastic materials like PP and ABS have their place—just not as the sealing surface.

If you’re not sure which scenario fits, talk to an engineer at a company with material expertise—like Trelleborg or its Minnesota Rubber and Plastics division. Bring your operating temperature, media, pressure, and whether the seal moves. A good supplier will ask those questions. And if they don’t? Find another supplier.