Film thickness (µm) and film materials compared: LDPE, LLDPE, HDPE, MDPE and OPP

What does micrometre (µm / micron) mean for plastic films?

In the film and packaging industry, material gauge is specified not in millimetres, but in micrometres (unit symbol: µm, often called 'micron' or 'my' in purchasing) [9]. One micrometre is one thousandth of a millimetre (1 µm = 0.001 mm, or 1,000 µm = 1 mm) [9].

Because film thickness directly determines basis weight and therefore resin consumption per 1,000 bags, it is – alongside width, length and polymer type – the primary cost and quality factor in any RFQ [8], [9]. Increasing or reducing thickness by just a few micrometres noticeably alters both puncture resistance (measured as the dart drop value in grams) and roll or carton weight [8], [9].

Specification in micrometres (µm)	Converted to millimetres (mm)	Practical example from the packaging range
under 15 µm (e.g. 8–14 µm)	under 0.015 mm	Very lightweight HDPE produce knot bags on rolls for loose fruit and vegetables; thin bin liners for light office waste [8], [17], [18]
25 to 45 µm	0.025 to 0.045 mm	Crystal-clear OPP bags for textiles and cards; medium-duty LDPE waste bags [9], [15], [16]
from 50 µm (e.g. 50–80 µm)	from 0.050 mm	Carrier bags permitted in Germany (from 50 µm); opaque Coex mailing bags; commercial refuse sacks [9], [14], [18]
80 to 200 µm	0.080 to 0.200 mm	Heavy-duty industrial and construction rubble sacks, VCI corrosion protection bags and hoods for heavy metal parts [2], [6], [9]

Key film polymers compared: LDPE, LLDPE, HDPE, MDPE and OPP

Depending on mechanical load, required clarity and heat-sealing behaviour, different polyolefins are used for bags and films [8], [16]:

Material	Structure & production	Typical properties	Main applications at Pakzeno
LDPE (Low Density Polyethylene)	High-pressure process (1,000–3,000 bar), highly branched molecular chains [8]	Soft, flexible, quiet feel, high puncture and tear-propagation resistance, easy to heat-seal [8]	Refuse sacks, VCI films and bags, Coex mailing bags, loop-handle carrier bags [6], [8], [14]
LLDPE (Linear Low Density Polyethylene)	Catalytic process (50–100 bar), linear chains with short branches [8]	Extremely stretchable, high tensile, puncture and seal seam strength [8]	VCI films, heavy-duty waste sacks, blends with LDPE and Coex films [8], [9]
HDPE (High Density Polyethylene)	Low-pressure process (1–50 bar), minimally branched chains, higher density [8]	Stiffer, rustling feel, high tensile strength at thin gauges, tears more easily once punctured [8]	Produce knot bags on rolls, thin bin liners, T-shirt carrier bags [8], [10]
MDPE (Medium Density Polyethylene)	Medium density between LDPE and HDPE [8]	Softer feel than HDPE with higher stiffness than LDPE [8]	Specialty bags and blended formulations [8]
OPP / BOPP (Oriented Polypropylene)	Polypropylene film stretched longitudinally or biaxially [16]	Crystal clear, brilliant gloss, crisp stiffness, good moisture barrier, excellent printability [15], [16]	OPP adhesive-flap bags, OPP flat bags for textiles, printed matter and food [15], [16]

Virgin material vs. recycled plastic (PIR and PCR)

Alongside polymer selection, buyers choose between virgin resin (prime grade) and recyclate (regranulate) [9], [10]:

• Virgin material: Required wherever maximum optical purity, crystal-clear transparency, controlled active-agent release (e.g. VCI corrosion protection films) or statutory rules for direct food contact under Regulation (EU) No 10/2011 (e.g. fruit and vegetable knot bags or OPP bakery bags) apply [2], [16], [25].
• PIR (Post-Industrial Recyclate): Recovered from clean, single-grade production offcuts from film extrusion and bag converting; delivers uniform mechanical performance while reducing virgin resin use [9], [10].
• PCR (Post-Consumer Recyclate): Reprocessed from used household and commercial packaging films; the primary choice for waste bags, refuse sacks and mailing bags, particularly when meeting ecolabel criteria such as the German Blue Angel (at least 80% recycled plastic in waste sacks) or municipal tender specifications [9], [10], [11].

Blown film extrusion, coextrusion and additives

Most PE bags and tubular films are produced by blown film extrusion: molten polymer granules are forced upward through an annular die and inflated with air into a film bubble [9], [26]. By adjusting the blow-up ratio and haul-off speed, machine- and transverse-direction film properties are precisely controlled [9], [26].

When two or three extruders feed a shared multi-layer die head on a coextrusion line, a Coex film is produced [9], [26]. This allows converters to combine a tough LLDPE core layer with heat-sealable LDPE skin layers or – as in Coex mailing bags – bond a white outer layer to a black opaque inner layer [9], [14]. Masterbatches and additives are dosed to tailor colour, opacity, slip, UV stabilisation or active corrosion inhibitors such as VCI [2], [9].

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