Key takeaways
- Family (PP-H, PP-R, or PP-B) and end-application
- MFI window — raffia and BOPP need low MFI (~3); injection thin-wall needs high MFI (40–60)
- For PP-B, the notched Izod target at the relevant service temperature
- For PP-R, the hot-water classification (PN-rating for pipe)
- Origin preference and Incoterms
Polypropylene is sold as three different families, and the choice between them is rarely a price decision. It is a property decision. Get it wrong and the part fails its first cold-storage shipment.
Homopolymer is pure propylene units, all the way down the chain. It is the stiffest and the highest-melting of the three (typical melt point ~165 °C), which is why it dominates raffia, BOPP film, woven sacks, and rigid food packaging where the part must hold its shape under hot fill.
Its weakness is impact, particularly at low temperature. PP-H goes brittle below about 0 °C. Anyone shipping PP-H crates to a cold climate without a copolymer overlay learns this once.
Random copolymer adds a few percent of ethylene units distributed evenly through the chain. The chain becomes slightly less crystalline, which trades a little stiffness for clarity, lower seal-initiation temperature, and better impact at room temperature.
PP-R is the standard for hot-water plumbing pipe (the green or red pipe sold under brand names like Aquatherm), for clear thin-wall containers, and for film where lower seal temperatures speed up the line.
Block copolymer is structurally different. It is essentially a PP-H matrix with islands of an ethylene-propylene rubber phase dispersed through it. Those rubber islands absorb impact energy. This is why PP-B is the default for automotive bumpers, battery cases, garden furniture, and any rigid part that must survive a drop or a winter shipment.
PP-B is hazier and slightly less stiff than PP-H, but its notched Izod impact at −20 °C is roughly an order of magnitude higher. That is the spec to compare on — not just MFI. Reading a polymer CoA correctly is the difference between buying the right grade and buying nine months of warranty claims.
- Family (PP-H, PP-R, or PP-B) and end-application
- MFI window — raffia and BOPP need low MFI (~3); injection thin-wall needs high MFI (40–60)
- For PP-B, the notched Izod target at the relevant service temperature
- For PP-R, the hot-water classification (PN-rating for pipe)
- Origin preference and Incoterms
If you are unsure between PP-H and PP-B, the question is simple: does the finished part ever live below 5 °C, and does it have to survive being dropped? If either answer is yes, you want copolymer. If the part lives indoors and stiffness matters more than impact, you want homopolymer.