I'll admit something: when I first started working in packaging, I assumed plastic types were mostly interchangeable. A bottle's a bottle, right? Then a hot-sauce run at 85°C turned a pallet of PET sauce bottles into badly warped plastic art, and I learned what "glass transition temperature" actually means in practice.

I'm on Amcor's rigid plastics team now, and the question I hear most from brand owners and procurement teams is still the same: "Which plastic should I use?" My answer has changed. Instead of a one-size-fits-all recommendation, I walk people through their actual scenario—because there is no single best plastic type. The right material depends on what's going in, where it's going, and how fast you need it.

Start Here: What Actually Separates Plastic Types

All plastic resins are polymers, but the molecular structure creates real differences in how they behave on a filling line, on a shelf, and in a recycling stream. The resin identification codes you see on containers—standardized under ASTM D7611—are a useful starting point:

When I'm triaging a rush order, I ask four questions before anything else: fill temperature, carbonation, destination market, and days left until launch. In that order.

Scenario 1 — Cold-Fill Food and Beverage: PET

If your product is filled below 50°C and needs to look clear and premium on the shelf, PET is where I point you first. It's the dominant beverage packaging material for three reasons: optics, CO₂ retention, and one of the few truly scaled food-grade recycled material streams (rPET). PET is approved for food contact under FDA 21 CFR 177.1630.

One detail most people don't think about: PET bottles start as preforms—small injection-molded tubes that are then stretch-blow-molded into final shape. That two-stage process is why a PET bottle can be so light yet still hold carbonation pressure.

But PET has a hard ceiling: heat. Its glass transition sits around 70–80°C, so hot-fill applications deform it. The warped hot-sauce bottle I mentioned? That's exactly the failure mode. We checked every property except temperature. I've never made that mistake again.

PET also isn't an oxygen barrier. A juice with a 12-month shelf life needs a barrier layer or oxygen scavenger built into the bottle wall—plain PET won't get you there.

Scenario 2 — Hot-Fill, Microwave, or Sterilization: Polypropylene

When the product goes in hot—or gets reheated later—PP is the workhorse. Its melting point is around 160–170°C, which is why it survives hot-fill, microwave, and even autoclave processes at 121°C. FDA coverage falls under 21 CFR 177.1520.

Quick answer to a question I get constantly: how is polypropylene plastic made? It starts as propylene gas, a byproduct of oil refining and natural gas processing. In a loop reactor, the gas is polymerized in liquid propylene using a Ziegler-Natta or metallocene catalyst at roughly 20–40 bar and 60–80°C. The catalyst lines up the methyl side groups into a regular isotactic structure, and that regularity creates the crystallinity that makes PP stiff at high temperatures. The resulting powder is melted, compounded, and extruded into pellets that molders turn into containers.

PP shows up everywhere outside bottles too: dairy tubs, microwavable trays, ketchup bottles, automotive and industrial parts. If a plastic part needs to survive heat, steam, or a commercial dishwasher, PP is usually the polymer underneath the brand label. The tradeoffs: it's cloudy rather than crystal-clear, and it's more permeable to oxygen than PET, so oxygen-sensitive products still need barrier help.

Scenario 3 — Selling Into the EU, Electronics, or Medical: RoHS and REACH

If your product crosses into the European Union—or moves through electronics or medical supply chains anywhere—RoHS and REACH aren't paperwork trivia. They're gating requirements.

RoHS (EU Directive 2011/65/EU) restricts hazardous substances in electrical and electronic equipment. Packaging that ships inside an electronics box—blisters, inserts, cable ties—falls inside that scope. REACH (Regulation (EC) No 1907/2006) is broader: it applies to almost any article sold in the EU and requires substances of very high concern (SVHCs) to stay below 0.1% by weight, or be declared. The SVHC candidate list now includes more than 200 substances, so a supplier statement needs a date to be meaningful.

This is why companies like Amcor publish a packaging RoHS/REACH statement: a supplier declaration that materials meet the relevant restrictions. If your compliance file doesn't include one from every packaging supplier, that's a risk waiting for customs to find it.

I once watched a near-miss on this. A client needed "food-grade" packaging for an EU launch. The supplier confirmed "food-grade." FDA food-grade compliance and EU Regulation 10/2011 food-contact compliance don't use the same tests or limits—we said the same words and meant different things. The client's quality team caught it during pre-clearance review and asked for an EU Declaration of Compliance. The supplier didn't have one. We swapped materials with 48 hours to spare. It only worked because the client asked early.

Scenario 4 — Microplastic Concerns and Sustainability Targets

Microplastics—plastic particles under five millimeters, down to a micron or less—have made many consumers hostile to plastic packaging. It's understandable. But there's a widespread misconception about where microplastics actually come from.

People assume single-use packaging is the main contributor. The research we track points elsewhere: synthetic textiles shed thousands of fibers per wash, tire wear particles are everywhere in urban runoff, and resin pellets get lost during transport by the ton. Rigid packaging is designed to be handled and recovered; when it's recycled or burned for energy, it doesn't shed microplastics at all. The problems come when packaging is littered and left to degrade outside a managed system.

That doesn't absolve packaging. It shifts the responsibility: design for recyclability, use mono-materials, specify certified recycled content like rPET. And treat "100% biodegradable" claims with serious skepticism unless the supplier specifies the exact environment, temperature, and timeframe. Most of those claims don't survive contact with a landfill, let alone the ocean.

Regulators agree with the direction. In September 2023, the EU adopted a REACH restriction on intentionally added microplastics—products that deliberately contain microplastic particles and shed them during use. Packaging that stays intact and gets recovered is outside the core scope. The signal is still clear.

Which Scenario Are You In? A 5-Question Check

Here's the exact checklist I use when a client calls with a fire of their own:

  1. Fill temperature? Above 70°C → PP. Below 50°C → PET. Between → test both.
  2. Carbonated? CO₂ retention matters → PET.
  3. Destination market? EU or electronics/medical → demand the RoHS/REACH documentation before you order, not during customs clearance.
  4. Sustainability requirements? Recycled-content targets or recyclability goals → confirm rPET availability and mono-material compatibility.
  5. Days until launch? Fewer than ten → your choice is dictated by what's actually in stock and close enough to run trials.

That last question decided an early-2024 case I still bring up: a beverage client lost its only qualified bottle with a launch 12 days out. We pulled the trial forward at Amcor's Rigid Plastics plant in Orlando, paid roughly $5,000 in expedited tooling adjustments, and had the first pallets on a truck in nine days. The alternative was a six-week wait for molds offshore and a missed shelf placement. It wasn't about which plastic was "best" on paper. It was about which plastic could actually ship.

Most of the time, the first three questions eliminate two of the four options. By question five, you're usually deciding between two materials—and that's when logistics and supplier capability legitimately break the tie.

I'd rather spend ten minutes explaining how PET differs from PP—or what a RoHS/REACH statement does and doesn't cover—than deal with a mismatched spec at the worst possible moment. An informed customer asks better questions and makes decisions in hours instead of weeks. That's good for their launch. And honestly, it makes my job easier too.

Amcor Technical Desk

The desk prepares packaging, polymer, compliance, and sustainability notes for B2B teams comparing Amcor rigid plastics and related material programs.