Polyethylene vs Polypropylene: A Procurement Checklist Using LyondellBasell's Website

I'm a procurement manager at a mid-sized plastics processor. We make components for the automotive and appliance industries, and I manage a polymer purchasing budget around $1.8 million a year—maybe $1.6 million, I'd have to check the last P&L. Over the last seven years, I've compared more resin grades than I can count. This is the checklist I use when someone asks me to compare polyethylene with polypropylene, or when we evaluate a material switch like PVC to HDPE.

Look, this isn't a chemistry lecture. There are enough experts on the technical side. My job is to make sure that when our engineers pick a resin, we understand what it actually costs—not just the price per pound.

Here's the thing: the LyondellBasell website can be a useful starting point if you know how to use it. But you need a method, or you'll drown in datasheets.

Who should use this checklist

Use this if you're sourcing PE, PP, or HDPE for a real application and need to compare product families. You've probably already heard generic things like “polypropylene is stiffer, PE is tougher.” That's true in a general sense, but it's not enough to make a buying decision.

You should also use it if you're answering the “pvc to hdpe” question. That switch is not just about material costs; it changes pressure ratings, installation, and chemical compatibility. The steps below still apply—you just need to take them more seriously.

Step 1: Define the application before you touch the website

Open a blank spreadsheet and list the resin uses you're considering. For each one, write down the must-have properties. I don't mean “strong and cheap.” I mean specifics:

• Continuous service temperature, and whether it's short-term peak or long-term maximum
• Impact requirements, including notch sensitivity if relevant
• Chemical exposure—acids, solvents, stress cracks
• Regulatory requirements, like food contact or flame retardancy
• Processing method, so you know which flow range to look for

This sounds obvious. I ignored it once. It cost us a $2,300 rework because I let a sales rep convince me that a general-purpose PP grade would work for a part that spent its life in hot, humid warehouse conditions. It didn't.

Checkpoint: if you can't name at least three measurable requirements, you're not ready to compare materials yet.

Step 2: Use the LyondellBasell website to find product families, not just grades

When I checked the LyondellBasell website in January 2025, the structure was fairly straightforward. You can search by product family or use the product finder to narrow down options. I start with two tabs open: one for polyethylene and one for polypropylene.

The point isn't to find “the best” grade. It's to see what families exist and where your requirements sit. For example, you'll see HDPE grades with different molecular weight distributions, PP copolymers versus homopolymers, impact-modified versions, and filled grades. Each one has a different cost structure.

Pay attention to the language. “Broad portfolio” sounds like marketing. What matters is whether they have a grade that matches your processing window. If the product finder lets you filter by melt flow rate or application, use that. If it doesn't, download the full datasheet and use your own spreadsheet.

Checkpoint: after this step, you should have no more than two or three grades per material family. If you have more, you're overcomplicating it.

Step 3: Compare polyethylene vs polypropylene using total cost, not just price per kilo

This is where things get interesting. Most people compare PE and PP by looking at typical mechanical properties and then calling a supplier for a quote. That's the right impulse, but it's incomplete.

Here's an example. HDPE has a density around 0.955 g/cm³. PP is around 0.90 g/cm³. All else being equal, PP gives you more parts per kilogram because it's lighter. But if your PP grade needs a thicker wall to get the same stiffness, you've just given back that advantage. The same logic applies when someone asks about PVC to HDPE: the cost per pound is only one line item.

What I mean is that the real material cost includes the part's weight, the processing conditions, the cycle time, and the scrap rate. A resin that costs 5% more per pound can end up being cheaper per part if it processes faster or runs with less waste.

Checkpoint: calculate cost per part, not cost per pound, and make sure your engineering team agrees on the assumptions.

Step 4: Check the datasheets for test conditions

LyondellBasell's datasheets are pretty thorough, but you have to know how to read them. A tensile strength number measured at 23°C means nothing if your part runs at 80°C. A “notched izod” test at room temperature won't tell you how the material behaves at -20°C.

Per LyondellBasell technical data, properties like tensile strength and flexural modulus are reported per standards such as ISO or ASTM. Compare numbers only when the standard is the same. Mixing ASTM and ISO values will give you bad conclusions.

Also, don't assume a typical value is a minimum. Datasheets often list typical values, and actual lots can vary. If your design depends on a specific property, ask for the spec range or a certificate of analysis. You're gonna want to verify the test method before you take any number seriously.

Checkpoint: for every property you listed in Step 1, you should know which test method and temperature was used.

Step 5: Ask for samples and validate before you commit

No matter what the datasheet says, you need to run the resin in your own process. In 2021, I thought I could save money by switching from one PP grade to a cheaper one with almost the same properties. The datasheets were nearly identical. The first production run disagreed. The “cheap” grade had a different lubrication package, and it caused severe die buildup. We lost a day and a half of production.

That's when I learned the value of requesting a small trial lot. LyondellBasell has distributors and technical teams that can help with this, but you have to ask. Don't expect a free pallet unless there's a real opportunity.

And here's something vendors won't tell you: the first quote you receive isn't necessarily the final price. Once you've qualified a material and shown that you're a serious buyer, there's usually room for negotiation. Not a huge amount—but it's not crazy to ask about annual volume rebates or improved payment terms.

Checkpoint: before signing a long-term contract, run a test lot through your actual process and measure first-pass yield.

Step 6: Include supply reliability in your cost model

This step gets overlooked because it's not on a datasheet. A cheap grade that arrives late is expensive. A material that creates supply chain drama because there's only one source is also expensive, even if the base price looks great.

LyondellBasell's global scale matters here. For a big buyer, that can mean dedicated supply and more consistency. For a smaller buyer, it might mean working through a distributor with local stock. The website won't tell you directly which path is right, but it can help you identify the product line and then contact the commercial team.

Total cost of ownership includes logistics, inventory, changeover time, and the risk of a supply disruption. Write that into the model.

Common mistakes in resin procurement

Mistake #1: Comparing the wrong grades. Polyethylene vs polypropylene isn't one comparison. A glass-filled PP can outperform an impact-modified HDPE in one test and fail in another. You need a specific grade comparison.

Mistake #2: Relying on generic “resin uses” charts. Those charts are good for a sanity check, not a purchase decision. Material selection is about your application, not a blog post.

Mistake #3: Ignoring density. I already mentioned this, but it deserves repeating. Buying polymer by weight and using it by volume means density is a cost driver. It's not just a lab value.

Mistake #4: Skipping the trial. A $500 test lot is cheap compared to a $15,000 production line problem. Do the trial.

Mistake #5: Trusting a number without a source. If someone tells you “HDPE is always cheaper than PP,” ask for the date, the region, and the grade. As of early 2025, I was tracking polymer market data through ICIS and similar services, and the spreads between PE and PP move around. They aren't fixed.

That said, this is from a procurement perspective. I'm not here to tell you which resin is “better” because it always depends on the application. I'm just here to make sure the cost model actually makes sense.