I've been handling packaging procurement for about six years now. And for the first two of those, I honestly thought I understood the plastic number system. You know the one — that little triangle with a number inside, usually on the bottom of a container.
I'd look at it, see a number, and think: "Okay, this one's recyclable." That was basically the extent of my knowledge.
Then, in September 2022, I ordered 5,000 rigid plastic containers for a pet treat line from one of our regular suppliers (who, at the time, sourced from a variety of large manufacturers including Amcor and Berry Plastics). The client's product was a high-fat, warm-filled pet treat — think a soft, oily chew that needed a container that wouldn't warp or leak at 120°F during summer transit.
I checked the spec sheet. It said "polypropylene." Great. I approved it.
What I didn't check — what I didn't even know to check — was what number that polypropylene actually was on the resin identification code.
That mistake cost $3,200. Here's what I learned.
The surface problem: People think the number means "recyclable"
This is where most of us start. You see a number — 1, 2, 5, 7 — and you assume it's a ranking system. Higher number = more recyclable? Or maybe harder to recycle? Or maybe banned?
Nope.
The number isn't a quality score or a recyclability rating. It's the Resin Identification Code (RIC), and it tells you what type of plastic the item is made from. That's it. Seven categories, established by the plastics industry back in 1988.
But here's the thing: almost everyone on the buyer side confuses this — including me, for way too long. Including your brand team, your compliance officer, and your logistics manager. We all think we know what the triangle means, but we're usually wrong about at least one critical detail.
What the numbers actually mean (the short version)
Before I get into the mistake I made, here's the quick rundown, because I wish someone had handed this to me six years ago:
- #1 (PETE or PET): Polyethylene Terephthalate. Clear, strong, good barrier. Standard for water bottles and peanut butter jars. Widely recycled.
- #2 (HDPE): High-Density Polyethylene. Opaque, chemical-resistant. Milk jugs, detergent bottles. Widely recycled.
- #3 (PVC or V): Polyvinyl Chloride. Rarely used in food packaging anymore. Not typically recycled curbside.
- #4 (LDPE): Low-Density Polyethylene. Flexible. Bread bags, shrink wrap. Not typically recycled curbside.
- #5 (PP): Polypropylene. Semi-rigid, heat-resistant. Syrup bottles, yogurt tubs (and my ill-fated pet treat container). Increasingly recycled, but still limited.
- #6 (PS): Polystyrene. Styrofoam. Disposable cups, takeout containers. Rarely recycled.
- #7 (OTHER): Everything else, including multi-layer or bioplastics. Almost never recycled.
Simple enough, right? But simple knowledge is dangerous when you think it's complete.
The deeper problem: The number tells you the resin, not the performance
Here's where I went wrong. I saw "polypropylene" on the spec sheet, and I thought, "PP is PP is PP." It's a 5, right? What's the risk?
The risk is that not all PP is created equal. The resin code only tells you the base polymer family. It doesn't tell you the molecular weight, the additives, the heat deflection temperature, or whether it was designed for hot-fill or cold-fill applications.
In my case, the container was PP, but it was a grade optimized for cold-fill. At 120°F, the sidewalls softened. The lids didn't seal. The pet treats — which were oily — started wicking through the material. The whole shipment was a loss.
(Honestly, I'm not sure why our supplier didn't flag this. My best guess is they saw "PP" on their own material list and assumed it would suffice. Communication failure on both sides.)
The deeper truth is this: the resin ID code is a material classification, not a performance guarantee. It tells you what family the material belongs to, not whether that specific formulation is right for your product, your fill temperature, your storage conditions, or your timeline.
What it cost us
Let me put numbers on this, because I track them:
- 5,000 containers — $1,800 material cost
- Labels and application — $600
- Shipping both ways and disposal — $800
- Total hard cost: $3,200
- Soft cost: A 2-week delay to the product launch, plus a very awkward conversation with the client about why their "approved" containers failed.
Worst part? I had checked the box. I had verified the material type. I just hadn't asked the right question: "What is the temperature tolerance of THIS specific PP grade?"
The real question you should ask (not just "what number?")
I'm not saying ignore the resin code. I'm saying it's the first question, not the last. Once you know it's PP (or PET, or whatever), you need to dig deeper.
Here's the checklist I now use (and yes, I keep it physically taped to my monitor after the third rejection in Q1 2024):
- Confirm the resin ID code — Yes, start here. Make sure everyone agrees on #1 vs. #5 vs. #7.
- Ask for the full material spec sheet — Not just "polypropylene." Ask for the specific grade and its properties: heat deflection temperature, impact resistance, chemical compatibility with your product.
- Clarify the application conditions — Fill temperature? Storage temperature? Duration at that temperature? Contact with oils, acids, or solvents?
- Get the manufacturer's data — If your converter is sourcing from a large producer like Amcor or Berry, they should be able to provide this. If they can't, that's a red flag.
- Test a sample under real conditions — Not just room temperature. Put it in your oven at 140°F for an hour. Fill it with your product and let it sit for a week. This is the step I skipped, and it cost me.
An informed customer asks better questions and makes faster decisions. I'd rather spend 10 minutes explaining this upfront than deal with a mismatched batch later. The number on the bottom is a starting point, not a conclusion. Know what you're actually buying.