I’ve Seen the Same Mistake for 6 Years
Over the past 6 years of tracking every invoice in our procurement system, I’ve noticed a pattern. When a new engineer or buyer asks for my help selecting a material, they almost always start with the same question: “What’s the price per kilogram?”
It’s the obvious question. It’s also the wrong one.
Here’s the thing: focusing on per-unit pricing for engineering polymers like PET, Nylon, TPU, or PPS is like buying a car based on the cost of the steering wheel. You’re missing the engine, the transmission, and the 30% of the budget that lives in the fine print.
Why “Simple” Cost Calculations Fail
The question everyone asks is “what’s your best price per kilo?” The question they should ask is “what is the total cost of using this material in my product, from order to disposal?”
The Hidden Factor Nobody Talks About
Most buyers focus on the raw material price and completely miss scrap rates. I want to say I learned this lesson quietly, but that’s not true. I learned it the expensive way.
In 2023, we switched a supplier for our acetal copolymer part. The new supplier quoted $0.50 less per kilo. It looked like a slam dunk on the spreadsheet. But within two months, our scrap rate on that line jumped from 2% to 7.5%. The material had slightly different shrinkage characteristics that our mold wasn’t tuned for. Every 100 parts, we threw away 5 more than before. That $0.50 savings evaporated. We ended up spending more per good part.
Lesson learned.
Processing Costs: The Budget Killer
Another blind spot is how the material behaves in processing. A material that is 10% cheaper but requires a slower injection cycle, higher processing temperatures, or more frequent purging is not a bargain. It’s a liability.
For example, when evaluating a TPE thermoplastic elastomer for a soft-touch overmold, one supplier’s price was attractive. But their material needed a 30-second longer cooling time. On a production run of 50,000 parts, that added over 400 hours of machine time. The cost of that lost capacity was far more than the material savings.
Your processing team might not flag this unless you ask. They are focused on making the part work, not on the cost of the cycle time.
The Real Cost of “Cheap” Material: A Case Study
This brings me to a specific example involving materials broadly like those in the Celanese portfolio, though the principle applies across the industry. Let’s say you’re choosing between two suppliers for a polypropylene part.
- Supplier A (Cheap): $2.00/kg. Standard lead time. Minimal tech support.
- Supplier B (Premium): $2.40/kg. Offers a customized grade with better flow characteristics and includes technical support for the first production run.
The numbers say Supplier A. My gut said stick with Supplier A. I was the one pushing the switch. It felt good to get the price down. But then the problems started.
Supplier A’s material, while cheaper, had a narrower processing window. Our molding team had to adjust settings constantly. We saw more flash. The parts had inconsistent gloss. We rejected a full batch of 10,000 parts because they failed our dimensional tolerance.
We had to run a second shift to catch up. The ‘savings’ disappeared into overtime pay and rework. That’s not including the cost of the delayed shipment to our customer, which strained that relationship.
I still kick myself for not insisting on a trial run. If I’d built a cost calculator based on processing stability and yield, I would have stuck with the premium supplier from the start.
The Cost of Qualifying a New Material
There’s another hidden cost that procurement often underestimates: the cost of qualification. When you switch to a new PPS or Nylon/EVA grade, you don’t just start buying it. You have to test it. You have to run trials. You might need to requalify the part with your customer. That process can take weeks and cost thousands of dollars in engineering time and lost production. The cheap material doesn’t compensate for that delay.
A Smarter Way to Evaluate Materials
So, what should you do? Stop looking at the price list. Start looking at the process.
The vendors who list all potential costs upfront—like material disposal fees, or the impact of their material on cycle time—are the ones I trust now. Even if their price per kilo is higher. Transparency is a signal of confidence.
Before you switch a material, buy 200 kilos of it. Run a production trial. Measure your cycle time. Track your scrap. Get your operators’ feedback. Then do the math. Compare the cost per good part, not the cost per kilogram. That’s your true benchmark. That’s the number that matters.
I’ve learned to ask ‘what’s the risk’ before ‘what’s the price.’ It’s saved me from more expensive mistakes than any spreadsheet ever could.