LDPE and LLDPE Films for Food: Thickness, Sealing and Barrier Basics

The short answer: LDPE and LLDPE are both polyethylene films used widely for food, but they are not interchangeable. LDPE seals easily at low temperatures, runs clear and soft, and is the default for liners, bread bags and shrink film. LLDPE has a linear backbone that makes it markedly tougher — higher tensile strength, better puncture and tear resistance, stronger seals once formed — which is why it dominates heavy-duty bags, frozen-food packs and stretch film, and why it lets you down-gauge to a thinner film at the same strength. Both are good moisture barriers but weak oxygen barriers, so neither suits oxygen-sensitive foods on its own. Specify by thickness (microns/gauge), seal temperature window and the barrier the product actually needs — and reach for a multilayer structure when polyethylene’s oxygen barrier falls short.

This guide breaks down each property, gives a thickness and selection table, and sets out the food-contact compliance language for your purchase order. It links up to the Food-Grade Packaging Resins hub and sideways to PP vs HDPE vs LDPE for food contact and Barrier resins and multilayer packaging (EVOH, PA).

LDPE and LLDPE: same family, different backbone

Both are polyethylene, but the chain architecture differs and that difference drives everything downstream:

• LDPE (low-density polyethylene) is made by high-pressure polymerisation, producing highly branched chains. The branches stop the chains packing tightly, lowering density and crystallinity. The result is a soft, clear, very flexible film with excellent low-temperature sealability. (Laird Plastics — LDPE Technical Guide)
• LLDPE (linear low-density polyethylene) is made by low-pressure copolymerisation of ethylene with a co-monomer, giving a mostly linear backbone with short-chain branches. The linear structure packs better and entangles more efficiently, so the film is tougher at similar density. (Polychemer — LLDPE vs LDPE, Gamut Packaging — LDPE vs LLDPE)

Mechanical properties: where LLDPE pulls ahead

Figures are typical ranges from the cited trade and manufacturer sources, not guarantees; confirm against the specific resin TDS. (Polychemer, Gamut Packaging)

In short: LLDPE is tougher and stronger; LDPE is clearer, softer and easier to seal. That is why most real food films are blends — a base of LLDPE for strength with LDPE added back for processability, clarity and seal. Shell notes LLDPE’s combination of puncture resistance, tensile strength, flexibility, tear resistance and seal strength is precisely what suits it to heavy-duty food bags, frozen vegetables, meat and poultry, ice bags, and stretch/shrink films. (Shell — LLDPE for food packaging)

Heat sealing

Sealing is where LDPE earns its place even in tough films:

• LDPE seals at lower temperatures (a typical processing window of ~160–260 °C) and has a wide, forgiving seal window, low hardness and a soft feel — excellent sealability. (Polychemer)
• LLDPE needs higher seal temperatures but, once formed, produces stronger seals with better hot-tack — important on vertical form-fill-seal lines where the seal must hold the product weight before it cools. (Polychemer, Gamut Packaging)

The practical answer on most lines is a sealant layer or LDPE/LLDPE blend that opens the seal window (from LDPE) while keeping seal strength and hot-tack (from LLDPE). If you are pairing the film with a packaging machine, the seal-jaw temperature and dwell come from the film, not the other way round — see Form-fill-seal vs pre-made pouch machines.

Thickness: microns, gauge and mil

Film is specified by thickness, in three unit systems that buyers mix constantly. Get the conversions straight:

(Hammer-IMS — Film Gauge Thickness, Unpakful — Mil vs Micron vs Gauge)

General thickness guidance for food and retail film:

• 15–30 microns: food wrappers, light retail bags, garment bags.
• 30–60 microns: carry bags, shrink films, flexible pouches.
• Thicker films give more strength, puncture resistance and barrier; thinner films cut cost and weight. (Ecoplast — LDPE film thickness, Polyfun — Packaging thickness & gauge)

Down-gauging: thinner film, same job

LLDPE’s strength is what makes down-gauging possible — reducing film thickness while holding mechanical performance. Done right, it cuts raw-material consumption by 15–30%, improving margin and lowering pack weight. (Sales & Plastics — SABIC LLDPE down-gauging) The caution: you cannot simply make the film thinner. Drop a multilayer structure from, say, 3.0 to 2.7 mils without upgrading the resin architecture and the film can fail barrier, tear and stiffness specs. (FlexPack Voice — Down-gauging multilayer film) Down-gauging is a resin-and-structure project, not just a die-gap change.

Barrier basics: what polyethylene does and does not do

This is where most food-film mistakes happen. Polyethylene films are judged on two transmission rates:

• WVTR (water vapour transmission rate) — how much moisture passes through. Lower = better moisture barrier.
• OTR (oxygen transmission rate) — how much oxygen passes through. Lower = better oxygen barrier.

For LDPE, WVTR is roughly 16–23 g/m²/24 h (tested at 38 °C, 90% RH on 1-mil/0.0254-mm film). That is a decent moisture barrier — but not a strong one relative to other polyolefins, and it gets worse the thinner the film. (ScienceDirect — Polyethylene Film overview)

The hard limit: polyethylene is a poor oxygen barrier. LDPE and LLDPE on their own will not protect oxygen-sensitive foods — coffee, nuts, cured meats, many snacks — for any useful shelf life. WVTR and OTR are balanced against the specific product’s needs when choosing a film. (gbpitester.com — WVTR & OTR testing)

When PE is not enough: go multilayer

To get an oxygen barrier you add a barrier layer in a multilayer (coextruded or laminated) structure — typically EVOH (ethylene vinyl alcohol) or PA (polyamide/nylon) — with PE as the sealant and moisture-barrier skin. The PE gives you the seal and the moisture barrier; the EVOH/PA gives you the oxygen barrier the PE cannot. This is the standard route for vacuum and modified-atmosphere food packs. We cover the structures, when each barrier is justified, and the cost in Barrier resins and multilayer packaging (EVOH, PA).

How the film is made: blown vs cast

Two extrusion routes dominate PE food film, and the route changes the film’s properties as much as the resin does.

• Blown film is extruded upward through a ring-shaped die into a tube (“bubble”), inflated with internal air and cooled by an external air ring. The biaxial stretch of the bubble gives balanced strength in both directions, which suits heavy-duty sacks, pallet wrap and tough food bags — typically LLDPE-rich. (Mid South Extrusion — Blown film extrusion, ScienceDirect — Blown film overview)
• Cast film is extruded through a flat die onto a chilled roll. It cools faster and more uniformly, giving higher clarity, gloss and gauge consistency — preferred for ultra-clear lidding, labels and high-gloss wraps. (CloudFilm — Cast vs blown film)

The shorthand on resin contribution holds across both routes: LDPE offers softness and seal, LLDPE boosts strength, HDPE adds stiffness and moisture resistance — which is why blends and coextrusions, not single resins, make up most real food films. (Mid South Extrusion) When you ask for clarity, you are often asking for cast or an LDPE-rich blown film; when you ask for puncture and tear, you are asking for blown LLDPE.

Additives: the part of the spec buyers forget

The base resin is only half the film. Functional additives decide whether it runs on your machine and protects your product:

• Slip agents lower surface friction so bags open and feed cleanly. Useful — but, as with closures, the slip chemistry can carry an organoleptic cost, so it matters for sensitive foods. (Plastics Engineering — Modifying slip with additives)
• Anti-block stops film layers fusing on the roll so the bag opens.
• Anti-fog keeps condensation from clouding the film over chilled produce and ready meals — a frequent requirement for fresh-food trays and bags. (CloudFilm — PE film classification)

Specify the additive package, not just the resin and thickness. Two films at the same micron and the same LLDPE base can behave completely differently on a packing line depending on slip and anti-block, and the additives are part of the food-contact compliance picture (next section).

A practical selection guide

Thickness bands are practical starting points from the cited sources; confirm against contents, distribution conditions and machine. (Ecoplast, Shell, shkpack — Food packaging films)

Food-contact compliance: what to put on the PO

Polyethylene films for food contact are addressed in the US under 21 CFR 177.1520 (Olefin polymers). Polyethylene for articles contacting food (not during cooking) must fall within density 0.85–1.00 g/cm³ and meet a maximum extractable fraction of 5.5% in n-hexane at 50 °C and maximum 11.3% soluble fraction in xylene at 25 °C; film used for packing or holding food during cooking has a tighter n-hexane limit of 2.6% at 50 °C. (eCFR — 21 CFR 177.1520) In the EU, food-contact plastics fall under Commission Regulation (EU) No 10/2011, with an overall migration limit of 10 mg/dm² and specific migration limits on listed substances. (eCFR 177.1520)

Two phrasing points we hold to:

• Food-grade is not the same as food-safe. A resin being food-grade describes the base polymer’s eligibility. The finished film’s safety depends on the full additive package (slip, anti-block, processing aids), the print/laminate, and migration testing of the actual structure. Specify the film as compliant with / meeting the requirements of 21 CFR 177.1520 and/or EU 10/2011, with certificates and migration data available on request — never “FDA approved” or “certified.” See Food-grade vs food-safe resins.
• For printed or laminated films, ask for the declaration of compliance on the finished structure, not just the base resin — inks, adhesives and barrier layers all count.

Matching the film to shelf life

The film question is really a shelf-life question. Work backward from how long the product must hold and what degrades it:

• Moisture-loss-limited (bread, fresh produce, baked goods): the enemy is the product drying out or, for produce, condensation. A single-layer LDPE/LLDPE film with the right WVTR and, for produce, anti-fog is often enough. Polyethylene’s moisture barrier is decent; its weakness here is rarely fatal.
• Oxygen-limited (coffee, nuts, cured meat, many snacks): the enemy is oxidation and rancidity. Polyethylene alone cannot deliver the oxygen barrier; you need a multilayer with EVOH or PA, with PE as the sealant and moisture skin. Specifying plain PE here guarantees short shelf life and customer complaints.
• Physical-damage-limited (frozen, heavy, sharp contents): the enemy is puncture and tear in the cold chain and in transit. LLDPE-rich blown film at adequate thickness is the answer; cold-temperature impact resistance is where LLDPE clearly beats LDPE.

Modified-atmosphere packaging (MAP), where the headspace gas is flushed and the pack must hold that atmosphere, almost always requires a barrier structure — the film has to keep oxygen out and the flush gas in. This is a case where down-gauging must be approached carefully: thinning a barrier structure can quietly raise OTR past the point where the MAP benefit is lost. (gbpitester.com — WVTR & OTR testing)

Common specification mistakes we see

• Specifying plain PE for an oxygen-sensitive food. Polyethylene is a poor oxygen barrier; coffee or nuts in a PE-only bag will go stale fast. Use a multilayer with EVOH/PA.
• Down-gauging by eye. Cutting a multilayer film’s thickness without re-engineering the resin/structure can fail barrier, tear and stiffness — the savings evaporate into returns. Treat it as a resin-and-structure project. (FlexPack Voice)
• Ignoring the additive package. Two films at the same micron and LLDPE base can run completely differently depending on slip, anti-block and anti-fog.
• Mismatching seal window to the machine. An all-LLDPE film with a high seal temperature on a line tuned for LDPE gives weak seals and leakers; a sealant layer or blend fixes it.
• Asking for “FDA approved film.” Ask for compliance with 21 CFR 177.1520 / EU 10/2011 and a declaration of compliance on the finished structure — inks, adhesives and barrier layers included.

How Innovote sources this

1. Start from the product and its enemy. Moisture loss, oxygen ingress, puncture in cold chain, or just clarity on shelf — the failure you are protecting against picks LDPE vs LLDPE vs multilayer before anything else.
2. Set the structure, then the thickness. Single-layer PE for simple jobs; multilayer with EVOH/PA where oxygen barrier is needed. Only then do we set microns, and we test down-gauging as a resin-and-structure question, not a die-gap one.
3. Tune the seal to the machine. We match the sealant layer/blend to your VFFS or pouch line’s jaw temperature, dwell and hot-tack need.
4. Pull the compliance pack: TDS, declaration of compliance to 21 CFR 177.1520 and/or EU 10/2011 on the finished structure, food-contact statement, and migration data where contents are aggressive.
5. Quote grade/structure, MOQ, lead time and a landed-cost path into Egypt, with the import documentation route. See the Food-Grade Packaging Resins hub.

We do not call a film “approved” or “certified.” We tell you what it is compliant with and hand over the data so your QA and NFSA file rest on documented ground.

FAQ

What is the difference between LDPE and LLDPE film?
Chain structure. LDPE is highly branched — soft, clear, easy to seal at low temperature. LLDPE is linear with short branches — tougher, stronger, better puncture and tear resistance, stronger seals at higher seal temperatures. Most food films blend both. (Polychemer)

Which is stronger, LDPE or LLDPE?
LLDPE. It has higher tensile strength (~15–30 MPa vs ~8–25 MPa), better puncture and tear resistance, and better cold-temperature impact — which is why it dominates frozen-food and heavy-duty bags and enables down-gauging. (Gamut Packaging, Shell)

How thick should my food film be?
As a starting point: 15–30 microns for wrappers and light retail bags, 30–60 microns for carry bags, shrink films and pouches. Thicker means more strength and barrier; thinner cuts cost. Confirm against contents and distribution. (Ecoplast)

Is LDPE a good barrier?
For moisture, it is decent but not strong (WVTR ~16–23 g/m²/24 h on 1-mil film). For oxygen, polyethylene is a poor barrier. Oxygen-sensitive foods need a multilayer structure with an EVOH or PA barrier layer. (ScienceDirect, gbpitester.com)

Can I down-gauge my film to save cost?
Often yes, using LLDPE’s strength — savings of 15–30% on material are realistic. But you cannot just make a multilayer film thinner; cut thickness without upgrading the resin/structure and you can fail barrier, tear and stiffness specs. Treat it as a resin-and-structure project. (Sales & Plastics, FlexPack Voice)

Is LDPE film food-safe?
LDPE/LLDPE grades can be compliant with 21 CFR 177.1520 and EU 10/2011, but food-grade is not the same as food-safe. The finished film’s safety depends on additives, print, laminate and migration testing of the actual structure. We supply the declaration of compliance on the finished structure and migration data. (eCFR 177.1520)

Blown or cast film for my food product?
Blown film (often LLDPE-rich) for toughness — heavy bags, frozen, pallet wrap. Cast film for high clarity and gloss with consistent gauge — lidding, labels, premium display wraps. The product’s priority, strength or clarity, points to the route. (CloudFilm)

Do I need anti-fog film?
If the pack holds chilled or fresh produce where condensation would cloud the film and hide the product, yes — anti-fog is a specific additive package, not a property of plain PE. Specify it explicitly. (CloudFilm — PE film classification)

Specifying a food film? Tell us the product, its shelf-life enemy (moisture, oxygen, puncture) and your packaging machine, and we’ll come back with the LDPE/LLDPE/multilayer call, thickness, seal window, MOQ, lead time and a landed-cost path — compliance pack attached. Start at the Food-Grade Packaging Resins hub, or read PP vs HDPE vs LDPE for food contact and Barrier resins and multilayer packaging.

Byline: Innovote Trade Desk. Property ranges compiled from manufacturer technical data and the cited trade and regulatory sources; film selection should be confirmed against the supplier’s current TDS and structure-level testing.