Who This Checklist is For (and When to Use It)

This isn't a textbook on polymer chemistry. It's a practical checklist I built after making—and meticulously documenting—about $14,000 worth of avoidable mistakes in material selection over the last 6 years. If you're sourcing materials for industrial prototypes, production parts, or even specialized projects like art installations or hydraulic systems, you've probably stood in front of a spec sheet wondering, "Wait, which one is right for this?"

Here's the honest truth: no material is perfect. I've wasted money on Dupont PTFE film that looked right on paper but was terrible for our specific application. I've ordered 4-polypropylene plastic pipes for a chemical line where we should have stuck with a standard fluoropolymer. I've even chosen the wrong silicone over a polyurethane for a seal, and that one cost me a weekend and a pissed-off client. So, I put this checklist together to help you avoid my learning curve. It has 5 steps, and step 3 is the one most people skip—I know because I used to be one of them.

Step 1: Define the Operating Environment First (Not the Material)

Most mistakes I see—and made—start with picking a material first. Someone says, "We need a Dupont Teflon snow and ice repellant coating for this outdoor sensor," and they go straight to finding a Teflon product. That's the wrong start.

Instead, define the environment. What are the exact conditions? Write them down. For our sensor project, the environment was:

  • Temperature range: -40°F to 140°F
  • Constant UV exposure
  • Direct contact with road salt and ice
  • Vibration from adjacent machinery
  • Need for a non-conductive surface

Only after you list the environment should you look at material properties. The Teflon coating was great for chemical resistance and release (snow/ice slide off? yes). But it was a nightmare for adhesion in our specific application because of the vibration and the plastic housing it was applied to. The coating simply didn't bond well. (Note to self: never assume a coating will stick to an unknown substrate without testing.)

Checkpoint: List the top 5 environmental stressors for your part. If you can't name 5, you haven't thought hard enough.

Step 2: Verify the Material's 'Natural' Compatibility (Don't Trust the Label)

I once ordered 4-polypropylene plastic pipes for a dilute acid line. The specification said "polypropylene" and the catalog said "good chemical resistance." Real talk: polypropylene is great for many dilute acids at room temperature. But our acid was at 160°F (not listed on the catalog page—I had to dig for the technical datasheet). The difference between room temperature and elevated temperature chemical resistance is massive.

Here's the thing: a lot of suppliers list generic pros. You need to check the specific chemical compatibility chart for the exact grade and at the relevant temperature. For resin sculptures, a different application entirely, I see people buying resins based on color or clarity alone, without checking UV stability or heat deflection temperature. The piece warps or yellows in a week. Same principle applies.

What I mean is: look for the official technical datasheet from the manufacturer—like Dupont's actual spec sheet for a PTFE grade, not a distributor's summary. The difference is usually night and day.

Checkpoint: Have you read the full technical datasheet (not the product page) for your material at your operating temperature?

Step 3: Test for 'Real World' Failure Modes (The Step Everyone Ignores)

This is the one I skipped for three years. I'd spec out a material based on tensile strength and chemical resistance, order it, and then it would fail because of something like stress cracking, creep, or galvanic corrosion. I don't have hard data on industry-wide failure rates, but based on my 6 years of orders, my sense is that about 70% of field failures I've seen are not from the primary properties (strength, chemical resistance) but from secondary ones (fatigue, UV aging, creep).

For example, consider polyurethane vs silicone. Many people pick silicone because it handles temperature better (usually). But in a dynamic seal application (like a soft rubber for a door gasket), polyurethane is often better at resisting abrasion and tearing. Silicone might be the 'range' choice—handles -100°F to 500°F—but it's way more prone to tearing under cyclic stress. The 'wrong' choice for temperature range might actually be the better choice for lifespan. I learned this the hard way on a $3,200 order of gaskets we had to scrap after 3 months because they all tore at the mounting point.

Checkpoint: What are the secondary failure modes? Creep? Tear? UV? Galvanic? List at least one.

Step 4: Consider the 'Total Cost of Selection' (Not Just Material Price)

Look, I'm not going to tell you to buy the most expensive Option A every time. That's bad advice. But I will tell you to factor in the cost of a potential failure. A few years back, I specified a standard polyurethane bushing for a machine that was just barely out of its recommended load range. It was $8 per bushing. A higher-grade Dupont PTFE/fiberglass composite bushing was $22. I went cheap. That single $8 bushing failed after 10,000 cycles and caused a $1,200 repair bill for the adjacent shaft.

The opposite also happens. I've seen engineers overspec a material—using a high-grade, expensive fluoropolymer for a low-temp, low-stress application where polypropylene would have been perfectly fine. That's wasted budget. So glad I learned to think in terms of "cost of the cheapest option that won't fail" rather than just "cheapest material."

Checkpoint: Calculate the potential downstream cost if this single material fails. Multiply that by the probability of failure. Compare that to the upgrade cost.

Step 5: Document the Decision (So You—or Your Team—Don't Repeat the Error)

I wish I had started doing this earlier. After the third rejection in Q1 2024 of a part we'd been making for a year (but with a new supplier for a second-sourced material), I created our team's pre-check list. But the format is just a shared Google Doc with columns: Application, Environment, Selected Material, Why, Test Results. That's it. We've caught 47 potential errors using this checklist in the past 18 months (including a batch of resin sculptures where the art team had chosen a non-UV-stable resin without checking, which would have been an absolute nightmare).

One of the items on that checklist is a simple question: "Did we test this material in a similar configuration before?" That question alone would have saved me about $5,000 in wasted material and 2 weeks of delays over the years.

Checkpoint: Have you written down the decision rationale for this material selection in a way that someone else can understand in 6 months?

Common Mistakes and Asks

Here are a few more things I've seen (and done):

  • Mistake 1: Skipping the 'Manual Logo' or marking requirement. In some regulated parts, you need a specific marking (like the 'Dupont manual logo' for certain compliance standards). I once ordered a batch of cast parts without verifying the marking mold. $750 wasted, plus a 1-week delay.
  • Mistake 2: Assuming resin for sculptures is all the same. It's not. A 'resin' can be polyester, epoxy, or polyurethane. Polyester is cheap but brittle for a large sculpture. Epoxy is strong but may yellow. Polyurethane is tough but can be sticky in the wrong durometer. Always specify the type.
  • Mistake 3: Forgetting about the 'Teflon' trade name. 'Teflon' is a brand name for PTFE and other fluoropolymers from Dupont. But 'Teflon snow and ice repellant' often refers to a specific coating dispersion, not the solid PTFE tape you buy at a hardware store. Verify you have the right form factor.

I don't have a perfect record—who does? But these 5 steps have dramatically cut down my expensive mistakes. If you're in a situation where you're choosing between materials, or if you've already made a choice and are having second thoughts, run through this list. It might save you a ton of time—and a few grand.