Haze Testing of Plastic Stretch Film: Standards, Methods, and Quality Control Guidelines

Haze testing of plastic stretch film quantifies the light-scattering behavior that governs the optical clarity of LLDPE cast and blown films used in pallet wrapping and protective packaging. Conducted in accordance with recognized standards such as ASTM D1003, ISO 14782, and GB/T 2410, haze measurement helps manufacturers verify clarity specifications, diagnose film defects, and support customer acceptance. This article explains the key definitions, sample requirements, test procedures, and practical applications of haze testing for stretch film products.

Technical Overview

Stretch film, most commonly produced from linear low-density polyethylene (LLDPE) by cast or blown extrusion, is valued not only for its elongation, puncture resistance, and load retention, but also for its optical appearance. In applications where wrapped goods must remain clearly visible, such as retail-ready pallets, display bundles, and machine-wrapped packages that require barcode scanning through the film, haze is one of the most important quality indices.

Haze is defined as the percentage of transmitted light that is scattered by more than 2.5 degrees from the direction of the incident beam when measured with a hazemeter or an integrating-sphere spectrophotometer. In practical terms, higher haze produces a milky, cloudy appearance that reduces the see-through quality of the film. The result is calculated as:

Haze (%) = (Diffuse transmittance / Total luminous transmittance) × 100

Because haze is not an intrinsic material constant, it depends on film thickness, crystallinity, additive content, and surface texture. Results must therefore always be interpreted together with the specimen construction and the specific test standard applied.

Testing Samples

Cast LLDPE Stretch Film

Cast films are quenched rapidly on a chilled roll, producing fine crystalline structures and smooth surfaces, so they generally exhibit the lowest haze, particularly when based on metallocene or octene-comonomer LLDPE resins. Machine-grade and hand-grade cast rolls at nominal thicknesses of roughly 10 to 35 µm are the most frequently submitted sample types.

Blown Stretch Film

Blown films cool more slowly on the bubble, developing greater crystallinity and slightly rougher surfaces, which raises haze compared with cast film of the same thickness. Both monolayer and co-extruded, typically three-layer, blown structures can be evaluated.

Pre-Stretched, Tinted, and Specialty Films

Pre-stretched films with reduced gauge after orientation, black or tinted security films, and films containing cling agents such as polyisobutylene can also be measured. For heavily tinted materials, total transmittance will be low, and it should be noted that the standard methods are intended for transparent and near-transparent plastics.

Sample Preparation and Conditioning

• Cut flat, wrinkle-free specimens of at least 50 mm × 50 mm, or sized to the instrument aperture, free of gels, scratches, and gauge bands.
• Handle specimens only with powder-free gloves; fingerprints, dust, and static-attracted particles add false haze.
• Condition at 23 ± 2 °C and 50 ± 10 % relative humidity for at least 40 hours in line with ISO 291 or ASTM D618 Procedure A before measurement.
• Test a minimum of three to five specimens taken from different positions across the web and report both individual and mean values.
• If single plies are too thin for stable readings and layers must be stacked, state the number of plies in the report, since haze increases with total thickness.

Testing Items

A standard optical test report for stretch film normally includes the following quantities and reference information:

• Haze (%): the share of transmitted light scattered at wide angles; the primary acceptance criterion for clarity.
• Total luminous transmittance (%): the overall light passed through the specimen, which affects the brightness of the view through the film.
• Diffuse transmittance (%): the scattered light component used to compute haze.
• Supporting data: nominal thickness, number of plies tested, process type (cast or blown), conditioning history, test standard, and instrument configuration.

Testing Methods

ASTM D1003

ASTM D1003, the Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics, is the most widely referenced method. Method A uses a dedicated hazemeter with an integrating sphere and a light trap that excludes regularly transmitted light so that only wide-angle scattered light is collected. Method B permits a spectrophotometer with an integrating sphere, with results computed for the specified illuminant and observer.

ISO 14782 and ISO 13468

ISO 14782 specifies the determination of haze for transparent plastics using integrating-sphere geometry and is commonly paired with ISO 13468-1, which covers total luminous transmittance. JIS K 7136 and JIS K 7361-1 are the corresponding Japanese national adoptions of these International Standards.

GB/T 2410

For the Chinese market, GB/T 2410 covers the determination of light transmittance and haze of transparent plastics and is technically aligned with the ASTM approach, making it suitable for domestic datasheets, incoming inspection, and conformity documentation.

Typical Test Procedure

• Verify instrument calibration using certified haze and transmittance reference standards, and perform an unobstructed blank-beam check.
• Mount the conditioned specimen flat across the transmission port without wrinkles, stretching, or trapped air.
• Record total transmittance, meaning all light passed, and diffuse transmittance, meaning scattered light with the regular beam excluded.
• Compute haze as diffuse transmittance divided by total transmittance, expressed as a percentage.
• Repeat for all specimens, average the results, and report the values together with thickness, ply count, standard applied, and instrument setup.

Applications

Haze data for stretch film are used throughout the value chain:

• Production quality control: continuous monitoring of extrusion temperature, cooling uniformity, and additive dispersion that can shift haze out of specification.
• Formulation development: comparing metallocene and conventional LLDPE grades, antiblock and slip agent levels, and co-extruded layer designs for optical performance.
• Process troubleshooting: a sudden rise in haze often signals melt fracture, increased crystallinity from cooling changes, die buildup, or excessive gauge variation.
• Retail and logistics requirements: verifying see-through clarity for display pallets and confirming that wrapped cartons, labels, and barcodes remain readable after wrapping.
• Procurement and certification: providing standardized optical data on technical datasheets and in reports issued by accredited third-party laboratories when independent verification is required.

FAQ

What haze value is considered acceptable for stretch film?

Acceptance limits are contractual rather than universal. Values below about 10 % are common targets for premium cast films, general-purpose machine films frequently fall between roughly 5 % and 20 %, and blown or heavily filled formulations may be higher. Because haze rises with thickness, specifications should always state the test thickness, and comparisons should be made at equal gauge.

Are haze and clarity the same property?

No. Haze describes wide-angle scattering that causes a milky loss of contrast, while clarity describes narrow-angle scattering and image distortion, meaning how sharply an object can be seen through the film. A film can combine low haze with poor clarity or the reverse, so critical applications may require both evaluations.

How does film thickness affect haze results?

Light scattering occurs within the bulk of the film and at both surfaces, so haze generally increases as thickness increases. Comparisons between films are meaningful only when samples are measured at the same nominal thickness or when the specification permits thickness-normalized reporting.

Why do haze results differ between laboratories?

Differences commonly arise from specimen handling, such as fingerprints, dust, or wrinkles, ply count and thickness differences, conditioning history, and instrument geometry or calibration. Aligning the test standard, specimen preparation, and reporting format minimizes variability between laboratories.

Can printed, tinted, or perforated stretch film be tested?

Only flat, transparent regions are suitable. Printed areas, perforations, and strong tints distort both transmittance and scattering measurements, so specimens should be taken from clean, unprinted zones and the sample condition clearly described in the report.

Is haze testing mandatory for stretch film?

Haze is not a regulatory requirement in most markets, but it is frequently demanded by brand owners, converters, and export customers as part of specification compliance, especially for retail-visible packaging. Testing through accredited third-party laboratories provides independent verification when required.