There is no material data sheet that gives you the same answer for every rush order. If you've ever tried to pick between a flexible silicone foam gasket, a rigid ABS foam board spacer, and a nitrile rubber molded seal, you know those three things are not interchangeable. They all look like 'rubber or foam' until they hit heat, oil, or repeated compression. Then they behave completely differently.

I have spent 12 years at a specialty materials distributor, most of them on the expediting side. I have handled 200+ rush jobs, from 'we need a replacement gasket in 48 hours' to 'the mold tooling was cut wrong and the line stops on Tuesday.' In my experience, the secret is not finding the fastest supplier. It is knowing which material can survive the application before you pay for next-day air.

Let's break this into four common situations.

First, Separate Materials by Job Type, Not by 'Rubber' or 'Foam'

The biggest mistake I see under deadline pressure is treating all gasketing materials as one category. (This was true in 2013, when I started, and it is still true today.) A part that looks like foam on your desk might be a soft sponge, a rigid board, or a dense molded rubber. Each one exists for a different reason.

Ask yourself three questions before calling a supplier:

  1. Will the part see high heat, flame, smoke, or fire rating requirements?
  2. Does the part need to spring back after being compressed repeatedly?
  3. Will it be exposed to oil, fuel, hydraulic fluid, or harsh solvents?

Your answers determine which scenario below fits.

Scenario 1: High Heat, Fire Risk, or Smoke Regulations → Momentive Silicone Foam

If the application is near a battery pack, motor, HVAC unit, or anywhere a flame and smoke rating is on the drawing, use a silicone foam. I routinely spec Momentive silicone foam for these jobs because the silicone backbone handles sustained heat far better than thermoplastic foams. ABS foam board, by comparison, softens and sags at temperatures that are still a normal Tuesday for silicone. And if the spec calls for low smoke or flame resistance, silicone foam is usually your first discussion, not an afterthought.

One example: In March 2024, a customer called at 4 pm with a failed gasket in an EV charger enclosure. The unit was going into a parking garage with strict smoke and fire requirements. The emergency replacement was a piece of Momentive silicone foam with adhesive backing. The part cost was maybe $140; the rush cut-and-ship fee was another $300. It arrived 36 hours later, and the line stayed on schedule. The alternative, using a non-rated sheet of ABS foam board machined from a scrap bin, would have been an immediate code failure. Missing the deadline would have meant a $50,000 penalty. (That is not an exaggeration. It was in the contract.)

I am not telling you silicone foam is the answer to every fire-adjacent job. But if you need flame and smoke data, a gasket that returns to shape, and a temperature range beyond what commodity plastics handle, start with silicone foam. Check the physical form on the Momentive official homepage before you order. As of January 2025, the product family pages list density, compression force deflection (basically, how stiff the foam is under a defined load), and available thickness. Don't rely on an old PDF from 2021; specs get updated.

Something to keep in mind: The few minutes you spend verifying the material data sheet is the cheapest insurance you have. A 12-point checklist I built after my third rushed mistake has saved us an estimated $8,000 in potential rework. Five minutes of verification beats five days of correction.

Scenario 2: Rigid Support, Short-Run Fixtures, or Non-Critical Prototypes → ABS Foam Board

Now let's talk about the foam board that is not a seal at all. ABS foam board is a rigid thermoplastic sheet with a foamed core. It is excellent for display panels, machining templates, shipping inserts, and prototype enclosures. It is also cheap, easy to tool, and usually available locally.

But it is not a gasket. It does not have meaningful compression recovery. If you compress it hard enough, it deforms and stays deformed. So use it where you need shape and stiffness, not where you need a cushion that bounces back.

For example, a client once needed a temporary spacer block to lift a heavy pump housing into alignment during installation. The rush order said 'foam' on the drawing, and someone almost ordered silicone foam because it was the first search result. The right call was ABS foam board: rigid, machinable, and half the price. (The silicone foam would also have worked in theory, but it would have squished under the load and made the alignment worse. Surprise, surprise—materials have different strengths.)

If this is a short-run prototype and the final production part will be something else, do not over-engineer your rapid solution. I can only speak to domestic distribution; if you are dealing with overseas sourcing, lead times and minimums change the calculus.

Scenario 3: Oil, Fuel, and Hydraulic Fluid Exposure → Nitrile Rubber Molding

This is where the conventional wisdom that silicone is the best rubber falls apart. Silicone is great for temperature and weatherability, but it is not the best choice for constant oil and fuel contact. For that, you want a nitrile rubber compression molded or injection molded part. Nitrile (NBR) is the workhorse material for seals and gaskets in lubricated equipment, gearboxes, fuel systems, and hydraulics.

So if your drawing says 'oil-resistant gasket,' do not reach for silicone foam just because you saw 'silicone' on the company homepage. At best, you get a shorter service life. At worst, you get swelling and extrusion under pressure. In my experience, a molded NBR part is almost always the answer when oil resistance is required and temperature stays within the elastomer's range (roughly under 100°C, depending on the compound).

Take this with a grain of salt: plenty of silicone seals fail in oil applications not because silicone is bad, but because the spec should have specified NBR from the start. The process—nitrile rubber molding—matters because it gives you a precise cross-section for complex seal profiles. Once you know the material is NBR, find a molder with in-house tooling or fast CNC-machined molds for prototypes. The expensive part is tooling; the expensive mistake is making the tool before confirming the elastomer grade.

The Grease Question: PTFE Grease vs Silicone Grease

Every third rush order seems to end with the same question: Which grease should we use on this thing I just spec'd? The answer depends on what is moving, what is nearby, and what could get contaminated.

Use silicone grease when...

You are lubricating rubber seals, plastic valves, low-speed bearings in wet environments, or any assembly where staying put and repelling water matters. Silicone grease is generally compatible with many elastomer compounds, and it is frequently used on silicone foam gaskets. It does not run away as easily as some petroleum greases, and it will not make rubber brittle like some mineral-oil greases can. (Don't hold me to this: compatibility charts still matter for exotic compounds, but as a first pass, silicone grease is the safer choice for rubber-to-rubber and rubber-to-plastic interfaces.)

Use PTFE grease when...

You are dealing with metal-on-metal friction, high loads, or any situation where the 'fish eyes' from silicone contamination would ruin a paint job, adhesive bond, or electrical contact. PTFE grease is chemically inert, handles high loads well, and does not create the same contamination problem in a paint shop. It is also the go-to for plastic gears or sliding mechanisms where a low coefficient of friction is needed.

My rule of thumb: If the grease will touch a rubber seal, silicone grease is usually the safe default. If it is for a metal bracket, threads, or a bearing, PTFE grease usually wins. If you are still unsure, call the seal manufacturer and ask for their compatibility list before you spec something that fails in the field.

How to Decide Which Scenario You're In

Here is the practical shortcut you can use on the way to the supplier:

There is no single best material, and anyone who tells you otherwise was not around when the plant shut down over an oil-resistant spec that got replaced with the wrong foam. Check your operating conditions, confirm the data on the Momentive official homepage, and if you are still not sure, ask a specialty distributor to look at the actual drawing. That little bit of diligence is what separates a cheap fix from an expensive lesson.