Reading a Resin Technical Data Sheet: MFI, Density, IV and Additives

A resin technical data sheet (TDS) tells you whether a grade will run on your line and perform in your part — but only if you read it correctly. The four numbers that decide most purchases are melt flow index (MFI/MFR), which indexes how easily the resin flows and, inversely, its molecular weight; density, which separates polyethylene grades and predicts stiffness; intrinsic viscosity (IV), the molecular-weight measure that defines PET and PA grades; and the additive package, which quietly determines processing and shelf behaviour. Crucially, a TDS lists typical values, not a guaranteed batch result — that is the job of a Certificate of Analysis. This guide explains each figure, why its test conditions matter, and how to compare two data sheets without being misled.

What a technical data sheet is — and is not

A TDS describes a grade: its typical properties, the test methods used, recommended processing conditions, and compliance statements. It is the manufacturer’s description of what the product is generally like (Pharmint — TDS glossary).

The single most important thing to understand: TDS values are typical/nominal, not specification guarantees for your specific lot. Typical values describe performance representative of the majority of the product but are not held to the rigour of a contractual specification (Analog Devices — testing “typical”). The document that proves what your batch actually measured is the Certificate of Analysis (COA) — issued per lot, showing the tested result against the agreed specification (SG Systems — COA).

When reading a COA, compare the specification column (the acceptable range) against the result column (the actual tested value); a compliant batch falls inside the spec (Sampan — spec sheet vs COA). Buying on a TDS alone, with no per-lot COA, means you are trusting “typical” with no contractual backstop. For any food-contact or critical application, agree the spec and require the COA.

Melt Flow Index (MFI / MFR): how the resin flows

MFI is the most quoted number on a polyolefin data sheet. It measures the mass of molten polymer, in grams, that flows through a standard die in ten minutes under a fixed temperature and load — reported in g/10 min (Wikipedia — melt flow index).

MFI and MFR are the same measurement

“MFI” (Melt Flow Index) is the older term used mainly in North America under ASTM; “MFR” (Melt Flow Rate / Melt Mass-Flow Rate) is the ISO term. They describe the same test — grams extruded through a standard die per 10 minutes at defined conditions (Pacorr — ASTM D1238 vs ISO 1133). The two governing standards are:

• ASTM D1238 (North American practice).
• ISO 1133 (international practice).

Both extrude a sample through a die under specified load and temperature and weigh the output. A practical difference: ASTM D1238 specifies a 2.095 mm die diameter, while ISO 1133 allows several die diameters (2.095, 1.18, 0.64 mm) (Pacorr — ASTM D1238 vs ISO 1133). For most polyolefin grades the everyday values are comparable, but for precise comparison confirm both sheets used the same standard and conditions.

The test conditions are part of the number

MFI is meaningless without its temperature and load. The same resin tested at 190 °C/2.16 kg gives a completely different number than at 230 °C/2.16 kg or 190 °C/5.0 kg (Pacorr — ASTM D1238 vs ISO 1133). Conventions differ by polymer:

So an HDPE MFI and a PP MFI are not on the same scale — you cannot compare a “2.0” PP to a “2.0” HDPE because they were measured at different temperatures. Always read MFI with its condition, written as e.g. MFI 8 g/10 min (190 °C/2.16 kg).

What MFI tells you about the resin

MFI is an inverse, non-linear (roughly logarithmic) proxy for molecular weight: high MFI means low molecular weight and low melt viscosity (flows easily); low MFI means high molecular weight and high viscosity (flows stiffly but is mechanically stronger) (Qualitest — MFI vs molecular weight). This is exactly why MFI maps to process:

• Injection moulding favours higher MFI (often ~10–30+, and for some PP 30–70 g/10 min) so the melt fills complex, thin-walled moulds quickly (Wikipedia — melt flow index).
• Film extrusion, blow moulding, profiles favour lower MFI (e.g. PP 2–12, some PE as low as 0.3–1 g/10 min) for the melt strength and dimensional stability the process needs (Wikipedia — melt flow index).

A common, costly error is buying a grade with the right resin family and density but the wrong MFI for the process — an injection grade that sags in a blow mould, or a film grade that fills a mould poorly. Match MFI to the process first.

Density: the dividing line for polyethylene

For polyethylene, density is the property that separates the grades and predicts much of their behaviour. It is measured at 23 °C per ASTM D792 or ISO 1183 (and the column-gradient method ASTM D1505), reported in g/cm³ (SpecialChem — polyethylene).

Density ranges and crystallinity per ScienceDirect — density polyethylene and Polymerdatabase — polyolefins.

The physics is direct: higher density means less chain branching, higher crystallinity, and therefore a stiffer, harder, less permeable polymer (ScienceDirect — density polyethylene). That is why HDPE (high crystallinity) makes rigid bottles and caps, while LDPE (low crystallinity, heavily branched) makes soft, clear film. Density is the first axis of PE grade selection; MFI is the second — together they pin down a polyethylene grade. See PP vs HDPE vs LDPE for food contact for how this plays out across applications.

For caps and pressurised closures, the data sheet should also carry ESCR (Environmental Stress Crack Resistance) alongside density — high-density grades can be more crack-prone under combined stress and chemical exposure, so cap grades are tuned for it.

Intrinsic Viscosity (IV): the number that defines PET and PA

For PET and polyamide, MFI is not the controlling figure — intrinsic viscosity (IV) is. IV is a solution-viscosity measurement that indexes molecular weight, reported in deciliters per gram (dL/g). Higher IV means higher molecular weight; lower IV means lower molecular weight (Infinita Lab — ASTM D4603).

For PET, the standard method is ASTM D4603: the resin is dissolved (typically 0.50% in a 60/40 phenol / 1,1,2,2-tetrachloroethane solvent) and flow times are measured at 30 °C in a glass capillary (Ubbelohde) viscometer (Infinita Lab — ASTM D4603). IV governs PET’s melting behaviour, crystallinity and tensile strength (Infinita Lab — ASTM D4603), which is why it is the headline number for choosing a PET grade.

Typical PET IV ranges

Bottle-grade PET IV generally falls in the 0.70–0.85 dL/g band; mineral-water preforms target around 0.80 ± 0.02 dL/g, and CSD/pressurised containers want ≥ 0.80, often 0.82 or higher (Chemate — PET IV value).

A practical warning: some sources quote far higher “PET IV” figures (3+ dL/g) — those refer to special high-molecular-weight or solid-state grades and do not apply to ordinary bottle resin. If a bottle-grade TDS shows an IV well outside ~0.70–0.86, query it. We cover IV selection in depth in PET resin grades by IV. For PA, IV (or relative/formic-acid viscosity) plays the same molecular-weight-indexing role; the higher the IV, the tougher and more melt-strong the nylon.

Additives: the package that changes how a grade behaves

Two grades with identical MFI and density can run and age very differently because of their additive package. The TDS may list these explicitly or only describe the grade as, for example, “slip/antiblock-modified film grade.” Common additive classes (ChannelPA — PE additives, Syensqo — polymer additives):

• Antioxidants / stabilisers — primary (phenolic) and secondary (phosphite) antioxidants protect the polymer from thermal-oxidative degradation during processing and in service, protecting melt stability and end-use shelf life.
• Slip agents — reduce surface friction so film unwinds and feeds smoothly (measured as coefficient of friction, COF).
• Antiblock agents — keep film layers from sticking to each other on the roll.
• UV stabilisers — UVAs (absorbers) and HALS (hindered-amine light stabilisers) protect parts exposed to sunlight (Syensqo — polymer additives).
• Nucleating / clarifying agents — speed and refine crystallisation in PP, improving clarity and cycle time.
• Antistatic agents — reduce static build-up on film and parts.
• Processing aids — improve melt flow and reduce die build-up.

For food-contact packaging the additive package is also a compliance matter, not just a processing one. Every additive in a food-contact layer must be permitted under the relevant regime, and the whole structure must meet migration limits. This is exactly where food-grade and food-safe diverge: a resin can be a food-grade additive package and still need migration testing to confirm the finished article is food-safe for a specific food, time and temperature. See food-grade vs food-safe resins for the distinction that should govern your purchase order.

Other lines on the sheet worth reading

Beyond the headline four, scan the data sheet for:

• Test method beside every value — a number without its ASTM/ISO method and conditions cannot be compared across suppliers. Two “MFI 5” values measured at different conditions are not the same grade.
• Mechanical properties — tensile strength, elongation, modulus, impact (each with its test method).
• Thermal properties — melt temperature, HDT/Vicat, and for food contact the use-temperature range.
• Moisture / drying — PET and PA are hygroscopic and the TDS will state drying conditions (temperature, dew point, time) that must be followed or the resin hydrolyses and IV drops in the extruder.
• Compliance statements — references to EU 10/2011, US FDA 21 CFR, REACH, etc. Read these as compliant with / meeting the requirements of — not as “approved” — and require the supporting declaration and per-lot COA.

Five ways a data sheet misleads buyers

Most resin purchasing mistakes trace back to a handful of repeatable misreadings. Watch for these:

1. Comparing MFI across different conditions. A “5” measured at 190 °C/2.16 kg and a “5” at 230 °C/2.16 kg are different grades. Normalise the condition before you compare (Pacorr — ASTM D1238 vs ISO 1133).
2. Treating typical values as a guarantee. Typical is not a spec — it is what the grade is usually like, with no contractual rigour (Analog Devices — testing “typical”). Without an agreed spec and a COA, you have no recourse if a lot drifts.
3. Ignoring the test method. A value with no ASTM/ISO method beside it cannot be trusted in a comparison, because two labs may measure “the same” property differently.
4. Buying density right but MFI wrong (or vice versa). For PE you need both axes correct — density for stiffness/permeability, MFI for the process. A correct-density grade with the wrong MFI will still fail on the line.
5. Applying the wrong IV expectation. Quoting a fibre IV for a bottle, or trusting a 3+ dL/g figure for ordinary bottle resin, leads to grade mismatches. Hold PET bottle IV to the ~0.70–0.86 band (Chemate — PET IV value).

A worked example: choosing between two HDPE grades

Suppose two HDPE bottle grades both look food-suitable. Grade A: density 0.954 g/cm³, MFI 0.7 g/10 min (190 °C/2.16 kg). Grade B: density 0.952 g/cm³, MFI 8 g/10 min (190 °C/2.16 kg). The densities are nearly identical, so stiffness and barrier will be similar — but the MFI gap decides the process. Grade A (low MFI, high molecular weight) has the melt strength for extrusion blow moulding a bottle; Grade B (high MFI, low molecular weight) flows easily and suits injection moulding a cap or closure (Qualitest — MFI vs molecular weight). Read only the density and they look interchangeable; read the MFI with its condition and they are for two different machines. This is the everyday discipline of reading a TDS: never one number in isolation, always the number with its method and against the process.

How Innovote sources this

A data sheet is a screening tool; the order is placed against a specification and proven by a COA. Our process:

1. We read the TDS against your process and part, not in the abstract — checking MFI against your forming process, density (for PE) against stiffness needs, and IV (for PET/PA) against the application band (e.g. ~0.80 dL/g for water bottles).
2. We normalise the comparison. Before comparing two suppliers we confirm both sheets used the same standard and the same test conditions (MFI temperature/load; density method). We do not compare a 190 °C MFI to a 230 °C MFI.
3. We separate typical from guaranteed. We agree a written specification (min/max ranges) for the load-bearing properties and require a per-lot Certificate of Analysis so you are buying to a contractual range, not to “typical.”
4. We check the additive package and food-contact basis. For food packaging we confirm the contact-layer additives are permitted under the cited regime and that migration compliance is documented — see migration testing and food-contact compliance and food-grade vs food-safe resins.
5. We document, never assert. Capability is phrased as compliant with / meeting the requirements of the cited standards, with certificates and specs available on request. We never describe a grade as “approved” or “certified” without the document behind it, and we make no health claims.

Send us a data sheet and your application; we’ll tell you whether the grade fits, what to put in the specification, and come back with grade, MOQ, lead time and a landed-cost path into Egypt.

Frequently asked questions

What is the difference between MFI and MFR?

They are the same measurement under different naming conventions. “MFI” (Melt Flow Index) is the older, mainly North-American/ASTM term; “MFR” (Melt Flow Rate) is the ISO term. Both report grams of polymer extruded through a standard die in 10 minutes at a defined temperature and load (Pacorr — ASTM D1238 vs ISO 1133).

Does a higher MFI mean a better resin?

No — higher MFI just means easier flow and lower molecular weight, which suits injection moulding but reduces melt strength and some mechanical properties (Qualitest — MFI vs molecular weight). Film, blow moulding and profile extrusion generally want lower MFI. “Better” depends entirely on your process — match MFI to the process, not to a number.

Why does the MFI condition (e.g. 190 °C/2.16 kg) matter?

Because MFI changes completely with temperature and load. The same resin gives different numbers at 190 °C/2.16 kg versus 230 °C/2.16 kg (Pacorr — ASTM D1238 vs ISO 1133). PE is usually tested at 190 °C/2.16 kg and PP at 230 °C/2.16 kg, so you cannot compare a PE MFI to a PP MFI, or any two MFIs measured at different conditions.

What IV should a PET bottle resin have?

Bottle-grade PET generally runs IV ~0.70–0.85 dL/g; mineral-water preforms target about 0.80 ± 0.02, and carbonated/pressurised containers want ≥ 0.80, often 0.82 or higher (Chemate — PET IV value). Fibre and thin film use lower IV. An IV far outside this band on a “bottle-grade” sheet should be queried.

Is a TDS the same as a Certificate of Analysis?

No. A TDS lists typical grade properties and is a description of the product in general; a COA reports the actual measured results for one delivered batch against the agreed specification (SG Systems — COA). For any critical or food-contact purchase, buy to a written spec and require the per-lot COA.

Why does the data sheet list drying conditions for PET and nylon?

Because PET and PA are hygroscopic and absorb moisture from air. If they are processed without drying to the stated conditions, the moisture causes hydrolysis in the extruder, which drops the IV and degrades mechanical properties. The TDS drying spec (temperature, dew point, time) is a processing requirement, not a suggestion.

Can two resins with the same MFI and density behave differently?

Yes — the additive package and the molecular-weight distribution (not just the average MFI indexes) both matter. Two grades with identical MFI and density can differ in clarity, slip, oxidative stability, crystallisation speed and food-contact compliance depending on their antioxidant, slip/antiblock, nucleating and stabiliser additives (ChannelPA — PE additives). This is why the additive section of a TDS — and the per-lot COA — matter as much as the headline numbers.

Which standards govern these tests?

MFI/MFR is measured to ASTM D1238 or ISO 1133; density to ASTM D792 / ISO 1183 (or ASTM D1505); and PET intrinsic viscosity to ASTM D4603 (Infinita Lab — ASTM D4603). A credible TDS names the standard beside each value; if it does not, ask — a number without its method cannot be compared across suppliers.

Tell us the spec; we’ll read the sheet with you

A resin data sheet only protects you if you read MFI, density, IV and the additive package with their test conditions — and back the typical values with a written specification and a per-lot COA. Send us the TDS and your application; we’ll tell you whether the grade fits, what to specify, and come back with grade, MOQ, lead time and a landed-cost path. Start at the food-grade packaging resins hub, or go deeper on PET resin grades by IV.

Byline: Innovote Trade Desk. Compliance statements describe materials as compliant with / meeting the requirements of the cited standards; certificates and specs available on request. This article is technical guidance, not a certification or a health claim.