The 7-Step Rush-Order Checklist for Dow Corning Silicone, Rubber, and TPU Replacements

I coordinate rush material orders for a gasket and seal distributor. In my role, 'normal lead time' and 'must be there yesterday' often show up in the same phone call. I've worked through maybe 300 of those calls in the last eight years—maybe 270, I'd have to check the system—and this is the checklist I use when someone needs a silicone rubber part, an O-ring, or a replacement tube in a matter of hours, not weeks.

This is not a design guide. It is a triage checklist for the moment when a machine is down, a customer is waiting, and you need a material decision that will survive. Seven steps, no fluff.

Who this checklist is for

Use this when you need a replacement rubber or silicone part, or a small length of flexible tubing, and the standard 2-6 week lead time is not an option. It also works when the part is not actually the problem—which, in my experience, is about 40% of the time.

It is not for full material development or high-volume production. If you're designing a new product, you should not be in a rush when you choose a compound. I get why people end up here anyway. Budgets and schedules are real. But this list stops you from making it worse.

Step 1: Confirm the failure mode before opening a catalog

The counterintuitive first step: don't start with Dow Corning silicone, TPU, or rubber. Start with what failed.

• Did the old part crack?
• Was it compressed and not springing back?
• Did it swell, harden, or soften?
• Was the fluid in contact hot, oily, or solvent-based?

I know this feels slower, but it saves the real emergency. In March 2024, a client called at 3 PM with a hydraulic test rig down. They assumed the O-ring was 'hard.' It wasn't hard—it had swelled because someone used the wrong cleaning solvent. We switched to a fluorosilicone-grade Dow Corning material, not a harder general-purpose rubber, and the test rig ran the next morning. The client's alternative was a $50,000 penalty clause on an external test window.

Based on our internal data from 200+ rush jobs, the biggest time leak is not manufacturing. It's choosing the right material twice. The first call should be 'why did it fail?' not 'what's the price?'

Step 2: Confirm geometry with a cross-section, not a photo

A photo only shows the face. For an O-ring or gasket, measure the cross-section, inside diameter, or groove width. 'About an inch' is not a dimension.

If the part is broken, tape it together and measure each segment. If you're in a hurry, cut a fit-check pattern from black foam board—we store ours under 'foam board black, 5mm' in the inventory system—to make sure the bolt holes or groove alignment are right. It's a pattern tool, not a gasket. You can also use it as a visual reference for the repair tech, but don't put it in service.

This is the step that gets skipped most often. People call with a photo and a part number, and the part number doesn't match the stamping. The photo doesn't tell you the cross-section. Measure before you order.

Step 3: Match the elastomer family to the environment

This is where Dow Corning silicones usually enter the conversation. Silicone rubber is commonly used when the application has broad temperature swings, UV/ozone exposure, or needs low compression set. According to Dow's published technical literature, many silicone grades maintain flexible service from roughly -50°C to 200°C depending on the formulation (Source: Dow product literature; verify current specifications). The sealing industry also uses ASTM D2000 line callouts to define heat and oil resistance. That classification is a useful starting point, but it does not replace a datasheet.

But silicone is not the default answer for every emergency. If you need abrasion resistance, hydrolytic stability, or a lower cost in volume, TPU or rubber may fit better. I use all three, and I don't have a favorite that works everywhere.

TPU vs Rubber Tubes: It's Not About Which Is 'Better'

For replacement tubes, the argument is usually TPU vs rubber tubes. To be fair, TPU is tough. It has strong tear and abrasion resistance and stays flexible in cold temperatures. Rubber tubes are still common because they're easy to bond, handle heat well, and are predictable in maintenance settings. Which one is better depends on what the tube carries, at what pressure, and at what temperature.

What was best practice in 2020 may not apply in 2025. Compound formulations have changed, and some TPU grades have improved. But the fundamentals—checking pressure, temperature, and chemical compatibility—haven't changed.

Step 4: Check durometer and compression set, not just color

Color tells you almost nothing. A black O-ring can be EPDM, NBR, silicone, or FKM. Durometer is only one number. Compression set tells you how much it will actually seal after it's squeezed. If you're replacing a Dow Corning silicone part, find the original grade and compare all the numbers in the technical data sheet.

I've never fully understood why some people choose a material based on shore hardness alone. Maybe it's because durometer is the first spec listed. If someone has insight, I'd love to hear it. In practice, I've seen a 70 Shore A NBR fail in three months while a 50 Shore A silicone survived years. The environment is the test, not the durometer.

Step 5: Check what's actually in stock before you commit to a material

A perfect material that has to ship from a factory in Germany is not a perfect material for a rush order. If the deadline is tomorrow, your best material is the one sitting in your distributor's warehouse, in the right dimensions, with the right durometer.

Search 'dow-corning' in the distributor portal, but don't stop there. They may stock other brands that cross-reference to the same spec. Also search by the part number stamped on the old part. For example, a customer once sent me a work order for a 'towhatsu prop o-ring'—a misspelling for Tohatsu—but that string was enough to find the right cross-reference in their file. We matched the dimensions, not the name.

If you don't know the exact grade, ask the supplier for the cross-reference list. In my experience, having three possible materials is safer than having one 'best' material that isn't available.

Step 6: Add a 48-hour buffer, even if no one wants to pay for it

Normal turnaround for custom silicone seals is 5-7 days. In reality, more like 7-10 days if the material isn't in stock. When someone promises 24 hours, ask how. If the answer is 'we have a half-finished part on the shelf,' that's different from 'we'll start cutting tomorrow.'

We lost a $30,000 order in 2023 because we trusted a vendor's 'overnight' promise without a backup plan. That's when we implemented our 'confirm the part is picked, packed, and labeled before we promise the client' policy. It sounds basic, but it missed once, and that was enough.

If there's a flight cutoff, pay the extra. We paid $800 extra in rush fees once to save a $12,000 project. It hurt. But the alternative was a $50,000 penalty clause. When I'm triaging a rush order, I'd rather explain a rush fee than a production stop.

Step 7: Write the material down and label the spare

Last step: put the actual material name and grade on the work order, the invoice, and the spare part bag. Otherwise, the next person will repeat this entire emergency.

Use a permanent marker to write 'dow corning silicone' or 'TPU' on the part. If it's a tube, mark the roll. I know it seems obvious. It's the step that gets skipped when the rush is over. In 2024, the same client called about the same application twice because the spare had no label. The second call took two minutes; the first had taken two days.

Three mistakes I keep seeing

The last 10% usually kills a rush order. Here are the three that cost real money.

1. Using a crossover chart as the final answer

A crossover chart tells you what might work. It does not tell you how a material will behave in your exact fluid, pressure, and temperature. Use it as a lead, then verify with the supplier or the technical datasheet.

2. Installing a fit-check part as a permanent fix

That foam board pattern? It's for checking dimensions, not sealing anything. I had a customer install a cardboard gasket because 'it fit.' It leaked. Use the pattern to confirm bolt holes and groove alignment, then install the real silicone part or the proper rubber/TPU replacement when it arrives.

3. Telling the customer 'it's guaranteed' when it isn't

Don't promise before you have a tracking number. And even then, say 'currently on track' instead of 'guaranteed tomorrow.' The most frustrating part of rush work is not the late deliveries—it's the promises that had no basis. You'd think people would learn, but pressure makes people say what the client wants to hear.

The fundamentals haven't changed: failure mode, geometry, environment, stock, lead time, documentation. The execution has to move faster than it did in 2020. That's all this checklist does.