Plastic Haze Testing: Standards, Methods, and Applications for Transparent Plastic Materials

Plastic haze testing quantifies the degree of light scattering in transparent plastic materials, a critical quality parameter for packaging films, optical sheets, lighting panels, and glazing products. This technical article explains the principle of haze measurement, applicable international standards such as ASTM D1003, ISO 14782, and GB/T 2410, specimen requirements, test procedures, and typical industrial applications.

Technical Overview

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 it passes through a transparent specimen. In plastic materials, haze is caused by surface roughness, scratches, microscopic voids, phase separation, crystalline structures, dispersed additives, and other internal or surface inhomogeneities. A higher haze value indicates a milkier, cloudier appearance and reduced see-through clarity, while a lower haze value indicates a clearer, more transparent material.

Haze testing is one of the most widely performed optical quality control tests for transparent and translucent plastics. It is typically measured together with total luminous transmittance, since the two parameters jointly describe the optical performance of a material: transmittance measures how much light passes through the specimen, while haze measures how that light is redistributed by scattering. Both parameters are expressed as percentages and are measured using a hazemeter or a spectrophotometer equipped with an integrating sphere and standardized illumination geometry.

Testing Samples

Flexible Films

Thin flexible films are the most common specimens for haze testing, including polyethylene (PE), polypropylene (PP), cast polypropylene (CPP), biaxially oriented polypropylene (BOPP), polyethylene terephthalate (PET), polyvinyl chloride (PVC), and polyamide (PA) films used in flexible packaging. Films are usually tested in single or multiple layers depending on the specification, and multi-layer measurements are frequently specified for laminated packaging structures.

Rigid Sheets and Plates

Rigid transparent sheets and plates such as polymethyl methacethacrylate (PMMA/acrylic), polycarbonate (PC), polystyrene (PS), polyethylene terephthalate glycol (PETG), and styrene-methyl methacrylate copolymer (MS) are tested for architectural glazing, lighting diffusers, signage, and machine guard applications. Because haze is strongly influenced by thickness, the reported result must always state the specimen thickness.

Molded Parts and Pressed Films

Injection-molded plaques, light guide panels, and optical components can be tested provided the measurement area is flat and free of curvature. For resin pellets, compression-molded or cast films of a defined thickness are prepared under controlled conditions so that the haze of the base polymer can be evaluated independently of processing variables.

Specimen Preparation and Conditioning

• Specimens must be flat, clean, and free of fingerprints, dust, oil, and visible scratches.
• The specimen size must fully cover the measurement port of the instrument, typically 50 mm × 50 mm or larger.
• At least three to five specimens should be tested and the results averaged.
• Specimens are conditioned prior to testing, commonly at 23 ± 2 °C and 50 ± 5 % relative humidity, in accordance with ISO 291 or ASTM D618, unless otherwise specified.

Testing Items

Commonly measured optical parameters for transparent plastics include:

• Haze: the percentage of transmitted light scattered more than 2.5 degrees from the incident direction, calculated as diffuse transmittance divided by total transmittance.
• Total luminous transmittance: the percentage of incident light that passes through the specimen, weighted by the photopic response of the human eye.
• Diffuse transmittance: the scattered component of transmitted light, reported directly or used to derive haze.
• Parallel transmittance: the unscattered component, used in some specifications to assess clarity.

Testing Methods

Standards and Reference Methods

• ASTM D1003: Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics. Method A uses a hazemeter; Method B uses a spectrophotometer with an integrating sphere.
• ISO 14782: Plastics — Determination of haze for transparent materials, which applies correction factors for instrument-related light losses.
• GB/T 2410: Chinese national standard for the determination of light transmittance and haze of transparent plastics, technically aligned with ASTM D1003.
• JIS K 7136 and JIS K 7361-1: Japanese standards covering haze and total luminous transmittance of transparent plastics.

Instrumentation and Procedure

A conventional hazemeter consists of a light source, a collimating optical system, an integrating sphere with a standard exit port, and a photodetector matched to the photopic spectral response of the human eye under a specified CIE standard illuminant, commonly Illuminant A with a 2-degree or 10-degree observer, or Illuminant D65 where required. The test sequence involves four measurements:

• T1: incident light reading with no specimen and the exit port closed by a light trap.
• T2: total transmitted light reading with the specimen in place and the light trap closed.
• T3: scattered light reading with no specimen and the exit port open.
• T4: diffuse transmitted light reading with the specimen in place and the exit port open.

Total luminous transmittance is calculated as (T2 / T1) × 100 %, and haze is calculated as [(T4 − T3) / T2] × 100 %. When the instrument scattering factor T3 is negligible, haze simplifies to the ratio of diffuse to total transmittance. Modern double-beam and scanning instruments automate the calibration, measurement, and calculation sequence, and regular verification with reference standards ensures traceability of results.

Factors Affecting Results

• Thickness: haze generally increases with specimen thickness because the optical path length and internal scattering volume increase.
• Surface condition: scratches, texture, dust, and anti-blocking or slip additives on the surface raise the measured haze.
• Internal structure: crystallinity, spherulites, voids, pigment particles, and phase-separated domains scatter light within the material.
• Orientation and residual stress: birefringence and density fluctuations in oriented films can contribute to light scattering.
• Instrument geometry and illuminant: differences between standards and instrument configurations can produce slightly different numerical results, so the applied standard must always be reported.

Applications

• Flexible packaging: quality control of PE, PP, BOPP, and PET films for food, pharmaceutical, and consumer packaging where high clarity enhances product presentation and visual inspection.
• Rigid packaging: evaluation of thermoformed containers, clamshells, and bottles made from PET, PS, PVC, and PP.
• Lighting and display: characterization of PMMA and PC diffuser sheets, light guide panels, and optical films for LED lighting, backlit displays, and touch panels, where haze is deliberately engineered to the required level.
• Automotive and transportation: incoming inspection of glazing, headlamp covers, instrument lenses, and transparent trim components.
• Construction: assessment of PC and PMMA roofing sheets, skylights, and greenhouse films where a defined balance of light transmission and light diffusion is required.
• Material development: comparison of resin grades, nucleating agents, clarifiers, processing conditions, and recycled content in research and development programs.

FAQ

What is the difference between haze and transmittance?

Transmittance measures the total amount of light that passes through a specimen, while haze measures the fraction of that transmitted light that is scattered away from the incident direction. A material can have high transmittance but high haze, appearing bright yet not see-through, such as a lighting diffuser. Conversely, a clear film typically has both high transmittance and low haze.

Why is a 2.5-degree scattering angle used in the definition of haze?

The 2.5-degree threshold corresponds to the integration sphere port geometry specified in the standards and approximates the angular limit beyond which scattered light is perceptible as milkiness or loss of image clarity to the human eye. Light scattered within this cone is treated as regular (direct) transmission.

Can colored or translucent plastics be tested for haze?

Haze is defined for transparent materials. Lightly tinted transparent plastics can generally be tested, but strongly colored or opaque specimens may fall outside the valid measurement range because very low transmitted light levels reduce measurement accuracy. The applicable standard should be consulted, and the applicability confirmed with the testing laboratory.

Does specimen thickness affect the haze result?

Yes. Haze increases with thickness, so meaningful comparisons require specimens of equal nominal thickness or explicit reporting of thickness with the result. Purchase specifications and test reports should always state the specimen thickness and the number of layers measured.

What haze values are considered acceptable for packaging films?

Acceptance limits depend on the application and contractual specification. High-clarity BOPP and PET packaging films are often specified with haze below 2 % to 3 %, while general-purpose PE films may be specified at higher levels. Translucent or diffusive products are intentionally specified with high haze values to achieve uniform light distribution.

Which organizations publish haze testing standards?

The principal standards organizations publishing haze and luminous transmittance test methods include ISO, ASTM International, the Chinese national standards system (GB), and the Japanese Industrial Standards (JIS) committee. Testing can be performed in-house or by accredited third-party laboratories with instrument calibration traceable to recognized reference standards.