LDPE blown film resin: melt index, density and how to order

This page covers LDPE for blown film. For every LDPE grade family, including shrink and clarity grades, see LDPE film grades. Coating grades are on LDPE extrusion coating resin.

Typical spec window

Typical ranges from published data sheets for grades in this window. Your grade’s own data sheet and the lot COA are what count.

What it’s used for

• Shrink and bundling film (fractional MI grades)
• Bread, produce and general food bags
• Overwrap and display bags (clarity grades)
• Liners and agricultural film
• The LDPE share of an LLDPE blend, where it steadies the bubble and adds clarity

How to tell grades apart

• Melt index. Below about 1 for shrink and heavy-duty film: more melt strength, but higher head pressure and less draw-down. About 1–2 for general-purpose bags. About 2 and up for clarity and thinner film.
• Density. Higher density in this window adds stiffness. Lower density gives a softer film that seals at a lower temperature.
• Slip. Usually erucamide or oleamide. Slip moves to the surface over hours to days, and too much hurts printing, sealing and lamination.
• Antiblock. Talc, silica or diatomaceous earth keeps the film from sticking on the roll, but raises haze.
• Additive-free grades. For film that will be printed or laminated, or where you dose your own concentrates.

What to put on your RFQ or PO

• Melt index with the condition. MI at 190°C / 374°F and 2.16 kg (ASTM D1238), nominal value and spec range.
• Density. By ASTM D1505, with a range, and the share of LDPE in your blend.
• Additives. Slip and antiblock type and level, or none; processing aid (say if it must be fluorine-free); antistat for dusty or electronics packaging; UV for agricultural film.
• Color. Natural, or the white or color concentrate you add and its carrier resin.
• Film properties you qualify on. Haze, gloss, dart, tear and COF, at the gauge you run.
• Gel limit. How gels are counted and the limit you accept.
• Food contact. The producer’s FDA letter for the exact grade (PE letters usually cite 21 CFR 177.1520), with your concentrates covered too.
• COA values to check. MI and density on every lot, plus gel count if the grade lists it.
• Packaging. Lined gaylords, 25 kg (55 lb) bags, bulk truck or railcar. LDPE pellets run about 31–36 lb/ft³.
• Quantity and release size. Total quantity, how much per release and how often.

A polymer chemist reviews every request and checks the grade against your process before we quote. Every prime lot from our suppliers ships with a COA, and orders start at one gaylord.

Equivalents and substitutes

• Another LDPE at the same MI, density and additives. The closest swap. Additive packages differ more than base resins, so check COF and blocking on the first rolls.
• More LLDPE in the blend. More dart and puncture at the same gauge, with less clarity and bubble stability. See LLDPE film resin.
• Metallocene PE. For down-gauging and a lower seal temperature. See metallocene PE and PP.
• Low-VA EVA. For a softer, clingier film. See EVA by vinyl acetate content.
• Extrusion coating LDPE. Not a substitute. The melt index is too high to hold a stable bubble.

Common processing problems

• Gels and fisheyes: gels in film
• Film that sticks to itself: film blocking
• A bubble that breathes or wanders: bubble instability
• Splits and punctures: film tearing or puncture
• Weak seals: heat seal failures
• Edge trim and regrind: using regrind

Common questions