Haze determination quantifies the degree of wide-angle light scattering in transparent packaging materials, directly influencing product visibility, shelf appeal, and compliance with material specifications. This article explains the principles, applicable standards (ASTM D1003, ISO 14782, GB/T 2410, JIS K 7361), sample requirements, test procedures, and calculation methods used for haze measurement of packaging films, sheets, and rigid containers. It serves as a practical reference for packaging engineers, quality control professionals, and buyers who need to verify optical performance through accredited third-party laboratories.
Technical Overview
Haze is defined as the percentage of transmitted light that, when passing through a specimen, deviates from the incident beam axis by more than a specified angle (typically 2.5 degrees) as a result of forward scattering. High haze values produce a milky, cloudy, or frosted appearance that blurs the view of the packaged product, while low haze values indicate sharp see-through clarity. Haze must not be confused with total luminous transmittance, which measures the overall fraction of light passing through the material regardless of direction.
In packaging applications, haze originates from bulk scattering within the polymer matrix, scattering at crystalline regions, surface roughness, fillers, additives, and interfaces in multilayer structures. Standardized haze determination enables objective comparison between materials, monitoring of production consistency, and verification against purchase specifications. The most widely referenced standards include ASTM D1003 (Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics), ISO 14782 (Plastics — Determination of Haze for Transparent Materials), GB/T 2410 (the Chinese national standard for light transmittance and haze of transparent plastics), and JIS K 7361. Measurements are performed using a hazemeter or a spectrophotometer equipped with an integrating sphere under specified illumination and photopic detection conditions.
Testing Samples
Flexible Films
Mono-layer and multilayer films such as PE, CPP, OPP, PET, PVC, and PLA films used for food pouches, lidding films, wrapping films, and barrier laminates. Specimens are typically cut to at least 50 mm squares or discs and should be free of wrinkles, folds, and surface contamination.
Rigid Sheets and Thermoforming Sheets
PVC, PET, PP, PS, and APET sheets used for pharmaceutical blister packs, thermoformed trays, and transparent windows. Surface texture introduced during extrusion or forming must be documented, as it strongly influences the measured haze value.
Container Wall Coupons
For bottles, jars, and tubs, flat coupons can be sectioned from the container wall in regions free of labels, embossing, and gate marks. Curved or heavily oriented sections should be avoided because curvature artificially redirects the light beam.
Coated and Laminated Specimens
Heat-seal coated films, metallized transparent films, and adhesive laminates should be tested in their final converted state, since coating thickness, adhesive layers, and interfacial haze all contribute to the total measured value.
Prior to testing, specimens should be conditioned in a standard laboratory atmosphere of 23 ± 2 °C and 50 ± 5 % relative humidity for a minimum of 40 hours in accordance with ISO 291 or ASTM D618, unless otherwise specified. Fingerprints, dust, and anti-block particles must be removed with lint-free wipes and, where appropriate, a suitable cleaning agent that does not alter the surface.
Testing Items
- Haze (percent of diffusely transmitted light relative to total transmitted light)
- Total luminous transmittance (percent of incident light transmitted through the specimen)
- Wide-angle light scattering behavior of transparent and translucent materials
- Optional related items: narrow-angle clarity, gloss, and color coordinates, which together characterize the full optical appearance of the packaging material
Testing Methods
Instrumentation and Principle
Testing is conducted with a hazemeter or a spectrophotometer fitted with an integrating sphere. A parallel light beam illuminates the specimen, and the sphere collects both the directly transmitted beam and the diffusely scattered light. By inserting a light trap that removes the unscattered beam, the instrument separately quantifies scattered and total transmission. ASTM D1003 specifies Standard Illuminant C with photopic response; ISO 14782 and GB/T 2410 also permit Illuminant D65 with the CIE 1931 standard observer, and results obtained under different illuminants should not be directly compared.
Measurement Sequence
The classic four-step reading sequence described in ASTM D1003 is as follows:
- T1 — incident light measured with the standard white reflectance body in position and no specimen
- T2 — total transmitted light measured with the specimen in place and the reflectance standard in position
- T3 — instrumental scattered light measured with the light trap in position and no specimen
- T4 — total scattered light measured with the specimen in place and the light trap in position
A minimum of three specimens per material is recommended, and each specimen should be measured at several positions to capture surface nonuniformity.
Calculation
Total luminous transmittance is calculated as Tt = (T2 / T1) × 100, expressed in percent. Haze is calculated as Haze = (T4 / T2 − T3 / T1) × 100, expressed in percent. The report should include individual and mean values, the test standard applied, illuminant and observer conditions, specimen thickness, and conditioning details. Modern automated hazemeters compute both quantities directly, but verification against the four-transmission method is recommended during instrument qualification.
Quality Assurance of Results
Instruments must be calibrated and zeroed before each test session, and reference filters or certified transfer standards should be checked periodically. Interlaboratory comparisons and routine verification by accredited third-party laboratories help ensure traceability and reproducibility of reported haze values.
Applications
- Food packaging: verifying the see-through clarity of films and thermoformed trays for retail shelf visibility
- Pharmaceutical packaging: confirming the optical quality of blister films where visual product inspection is required
- Consumer goods packaging: comparing transparent window films, folding carton windows, and shrink sleeves
- Material development: evaluating the effect of resin grade, slip agents, anti-block additives, crystallinity, and gauge on optical performance
- Incoming inspection and supplier qualification: objective acceptance criteria for haze in purchase specifications
- Photovoltaic and electronics packaging: optical evaluation of encapsulant films and protective cover films where light diffusion must be minimized
FAQ
What is the difference between haze and transmittance? Transmittance measures how much light passes through the specimen in total, while haze measures the fraction of that transmitted light that is scattered more than 2.5 degrees off axis. A material can have high transmittance yet high haze, appearing bright but blurry.
What haze value is acceptable for packaging? Requirements depend on the application. Premium clarity films such as biaxially oriented PET often specify haze below 2 to 3 percent, general-purpose PP films commonly fall between 1 and 6 percent, and translucent or diffusion films intentionally exceed these values. Acceptance limits should be agreed in the material specification.
Which standard should be used? ASTM D1003, ISO 14782, GB/T 2410, and JIS K 7361 are all recognized, and they are broadly harmonized in principle. However, differences in illuminant, instrument design, and calculation details mean results are only comparable when the same standard is applied.
Does thickness affect haze? Yes. Scattering increases with optical path length, so haze rises with specimen thickness. Haze values are only valid when specimen gauge is reported and compared materials share a similar thickness.
Can haze be tested on curved containers? Direct haze measurement requires flat specimens. For bottles and jars, flat coupons cut from the container wall are tested, and the sampling location must be stated in the report.