Key takeaways
- Polypropylene sells as three families and the choice is a property decision, not a price one — the wrong family fails its first cold-storage shipment.
- Homopolymer (PP-H) is the stiffest and highest-melting (~165 °C) — raffia, BOPP film, woven sacks, rigid hot-fill packaging — but turns brittle below ~0 °C.
- Random copolymer (PP-R) adds a few percent ethylene for clarity, lower seal-initiation temperature and better room-temperature impact — hot-water pipe and clear thin-wall.
- Block/impact copolymer (PP-B) disperses an ethylene-propylene rubber phase in a PP-H matrix for roughly 10× the notched Izod at −20 °C — bumpers, battery cases, anything dropped or shipped cold.
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.
Frequently asked
Questions on the desk
What is the difference between PP homopolymer and copolymer?
Homopolymer (PP-H) is pure propylene units — the stiffest and highest-melting polypropylene, but brittle in the cold. Copolymers add ethylene: random copolymer (PP-R) distributes a few percent evenly for clarity and lower seal temperature, while block/impact copolymer (PP-B) disperses rubber islands through a PP-H matrix to absorb impact energy.
Which polypropylene survives cold temperatures?
Block/impact copolymer (PP-B). Its notched Izod impact at −20 °C is roughly an order of magnitude higher than homopolymer's, which goes brittle below about 0 °C. Any rigid part that must survive a drop or a winter shipment should be PP-B.
What is PP-R (random copolymer) used for?
Hot-water plumbing pipe (the green/red PN-rated pipe), clear thin-wall containers, and film where a lower seal-initiation temperature speeds up the line.
Homopolymer or copolymer — how do I decide?
Ask whether the finished part ever lives below 5 °C and whether it must survive being dropped. If either answer is yes, choose a copolymer. If the part stays indoors and stiffness matters more than impact, choose homopolymer — and compare notched Izod at the service temperature, not just MFI.
General market commentary from the OmniaStrata desk, provided for information only. It is not legal, financial, tax, or trading advice, and it is not an offer or a commitment to any terms. Figures such as price ranges, spreads, financing costs, and credit periods are illustrative market context, not OmniaStrata's rates or terms. Actual contract terms — including price, payment instrument, credit, insurance, and Incoterms — are agreed in writing on a per-transaction basis and at OmniaStrata's discretion. Market conditions change; figures reflect the publication date.