High-density polyethylene is one of the highest-volume polymers traded anywhere, and one of the easiest to buy wrongly. HDPE is not a single material: it is a family of grades tuned for specific processes, and a grade built for blow moulding will not run on a film line. Two numbers do most of the work in telling them apart — melt flow index and density — and understanding them is what lets you compare offers properly. This is a plain-English reference for anyone buying or selling HDPE, prime or recycled.
What does MFI mean on an HDPE grade?
Melt flow index (MFI, sometimes MFR) measures how easily the molten polymer flows, in grams extruded in ten minutes under a set weight at a set temperature. Low MFI means high molecular weight, stiffer melt, better mechanical and stress-crack performance, and a harder material to push through a machine. High MFI flows easily and fills complicated moulds.
The trap is that MFI is meaningless without its test condition. HDPE is quoted at 190°C under 2.16 kg (often written MFR2), 5 kg (MFR5), or 21.6 kg (the high-load index, HLMI). The same resin gives wildly different numbers under each. If an offer says only "MFI 0.35", ask which load — a 0.35 at 2.16 kg and a 0.35 at 21.6 kg are not remotely the same material.
What are the main HDPE grade families?
Grades are built around the process they are intended for:
- Blow moulding — low MFI, typically around 0.2 to 0.8 at 2.16 kg. Bottles, drums, jerricans, IBCs and tanks. Melt strength matters more than flow.
- Injection moulding — higher MFI, commonly 4 to 20 or above. Crates, caps and closures, housewares, thin sections.
- Blown film — very low MFI high-molecular-weight grades, usually quoted at 21.6 kg. Carrier bags, liners, heavy-duty sacks.
- Pipe — bimodal pressure grades classified as PE80 or PE100, quoted at 5 kg. The number is the minimum required strength in MPa over a fifty-year design life, so PE100 is the higher-performance class.
- Sheet and extrusion — mid-range grades for board, geomembrane and profile.
Density is the second axis. HDPE runs roughly 0.941 to 0.965 g/cm³; higher density gives more stiffness, hardness and chemical resistance and slightly less impact toughness.
How do prime, regrind and recycled HDPE differ?
Condition sits alongside grade, and both belong on any serious offer:
- Prime — first-quality virgin resin to the producer's datasheet, with a known grade name and MFI. Fully predictable, highest price.
- Near-prime and off-spec — virgin material with a deviation, a wide-spec run, or a packaging or documentation problem. Good value if you know which property is off and whether it matters for your process.
- Regrind — ground production material or products, usually from a single known source. Drum, crate and pipe regrind are common. Consistent if the source is clean and single-stream.
- Recycled — reprocessed post-industrial or post-consumer material, sold as flake, regrind or repelletised granule. Quality varies enormously, so source and washing matter most here.
Colour is a genuine value driver in recycled HDPE: natural runs above mixed colour, which runs above black, because natural can be coloured to anything downstream and black cannot.
What drives the price of HDPE?
Several factors move at once:
- The virgin market — recycled and off-spec HDPE track virgin resin at a discount that widens when virgin is long and tightens when it is short.
- Grade fit — a blow-moulding grade sold to an injection moulder is worth less than its datasheet suggests, because the buyer pool for it is smaller.
- Condition and consistency — single-source regrind commands more than mixed, because the buyer can predict it.
- Colour and cleanliness — natural over mixed over black; washed over unwashed; pellet over flake over unground.
- Food-contact or regulatory approval where it applies, which can be worth more than every technical property combined.
- Quantity, location and incoterm — a full load prices differently from a parcel, and an ex-works price is not a delivered one.
Because these move independently and change constantly, no fixed price list stays right for long. HDPE is best priced against live offers for material of the same grade, condition and colour.
How does Prime Polymers handle HDPE?
HDPE listings sit on the same board as every other polymer, each stating type, grade, condition, quantity, location, incoterm and the seller's own asking price per tonne, so you can compare like for like. Prices are shown exactly as sellers enter them — never computed, adjusted or benchmarked by us. Browsing is free and open without an account. If nothing on the board fits what you need today, a Wanted post puts your specification and tonnage in front of sellers so they come to you. Prime Polymers is operated by ARC Polymers Ltd, a UK polymer trading company.
Frequently asked questions
- What is the difference between PE80 and PE100?
- Both are HDPE pressure pipe classifications. The number is the minimum required strength in MPa over a fifty-year design life at 20°C, so PE100 is the higher-performance class and allows a thinner wall or a higher pressure rating for the same pipe. PE100 grades are typically bimodal resins and are quoted at 5 kg load.
- What MFI do I need for HDPE blow moulding?
- Blow-moulding grades are usually low flow, broadly 0.2 to 0.8 g/10min at 190°C and 2.16 kg, because melt strength matters more than flow. Injection grades run far higher. Always confirm the test load quoted, since the same resin reads very differently at 2.16 kg, 5 kg and 21.6 kg.
- Is natural HDPE worth more than black?
- Generally yes, in recycled and regrind material. Natural can be pigmented to any colour downstream, so it serves more buyers; black is already committed. Mixed colour typically sits between the two. The gap varies with the market rather than being fixed.
- What is the difference between HDPE and LDPE?
- Density and branching. HDPE is roughly 0.941 to 0.965 g/cm³ with little chain branching, making it stiff, strong and chemically resistant. LDPE is around 0.910 to 0.925 g/cm³ with heavy long-chain branching, making it soft, clear and easy to extrude. They are not interchangeable and price differently.
- How can I see what HDPE is trading at?
- Check live offers rather than a dated list. On Prime Polymers each HDPE listing shows the seller's asking price per tonne next to the grade, condition, quantity, location and incoterm, so you can compare what is genuinely on offer. If nothing matches, post a Wanted requirement and let sellers approach you.