Haze index testing is a critical optical quality control measurement for transparent and translucent plastic materials, quantifying the percentage of transmitted light that is scattered by a specimen. This technical article explains the definition of haze, applicable international standards such as ASTM D1003, ISO 14782, and GB/T 2410, specimen preparation requirements, instrument-based test procedures, and typical industrial applications for films, sheets, and molded plastic products.
Technical Overview
Haze is defined as the percentage of transmitted light that, in passing through a plastic specimen, is scattered by more than 2.5 degrees from the direction of the incident beam. It is calculated as the ratio of diffuse transmittance to total luminous transmittance, expressed as a percentage. A high haze value causes a milky or cloudy appearance and reduces the ability to see sharp images through the material, while a low haze value indicates high optical clarity.
Haze is one of the most widely specified optical performance indicators for transparent plastics, alongside total luminous transmittance and regular transmittance. It directly affects visual quality, product aesthetics, light diffusion behavior, and end-use functionality. Manufacturers of packaging films, lighting covers, display windows, and glazing materials routinely specify haze limits in material datasheets and purchase agreements.
The principal test standards governing haze measurement of plastics include:
- ASTM D1003 — Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics
- ISO 14782 — Plastics: Determination of haze for transparent materials
- ISO 13468-1 — Plastics: Determination of the total luminous transmittance of transparent materials
- GB/T 2410 — Chinese national standard for determination of luminous transmittance and haze of transparent plastics
- JIS K 7136 and JIS K 7361-1 — Japanese industrial standards corresponding to ISO 14782 and ISO 13468-1
Testing Samples
Flexible Films and Packaging Materials
Plastic films such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), and multilayer laminated structures used for food packaging, protective films, and overwrap applications are commonly submitted for haze testing. Film specimens should be flat and free from wrinkles, creases, or trapped air, as these defects artificially increase measured haze.
Rigid Sheets and Panels
Transparent and translucent flat materials, including polymethyl methacrylate (PMMA), polycarbonate (PC), polystyrene (PS), and rigid PVC sheets, are tested as received or cut to size. Surface condition is critical; specimens must be clean and must not carry scratches, dust, oil, or protective film residue.
Injection-Molded Plaques and Molded Parts
For resin characterization, haze is measured on injection-molded or compression-molded optical plaques with well-defined mold surface finish and thickness. Molded components such as lighting lenses, windows, and covers can also be evaluated if a sufficiently flat test area exists.
Resin Granules and Pellets
Raw polymer granules cannot be tested directly. They must first be dried and processed into plaques of specified thickness under controlled molding conditions, after which the plaques serve as the test specimens.
Typical specimen requirements include a minimum size of approximately 50 mm by 50 mm (or a diameter large enough to fully cover the instrument aperture), a representative and clearly documented thickness, and conditioning at standard laboratory atmosphere (23 ± 2 °C and 50 ± 10% relative humidity) prior to measurement, in accordance with ISO 291 or ASTM D618.
Testing Items
A standard optical characterization report for transparent plastics typically includes the following measured and calculated parameters:
- Haze value (percentage of wide-angle scattered transmitted light)
- Total luminous transmittance (ratio of total transmitted light to incident light)
- Diffuse transmittance (scattered component of transmitted light)
- Regular (specular) transmittance (light transmitted without deviation)
- Test specimen identification: material grade, thickness, surface condition, and molding history
- Instrument and illuminant information, test standard applied, and number of specimens tested
Testing Methods
Hazemeter Method (ASTM D1003 Method A)
The most common approach uses a dedicated hazemeter based on an integrating sphere optical system. The instrument performs four sequential measurements: incident light flux, total transmitted flux, light scattered by the instrument itself, and light scattered by both the instrument and the specimen. Total transmittance is calculated from the ratio of transmitted to incident flux, while haze is calculated by dividing the specimen-attributable diffuse flux by the total transmitted flux. The measurement uses a specified standard illuminant with a photopically corrected detector to match the response of the human eye.
Spectrophotometer Method (ASTM D1003 Method B / ISO 14782)
A recording spectrophotometer equipped with an integrating sphere can be used to obtain transmittance data across the visible wavelength range. Haze and transmittance values are computed from spectral scan data with appropriate illuminant and observer weighting. This method provides additional spectral information useful for colored or tinted materials where visual weighting significantly affects the result.
Test Procedure Summary
- Condition specimens at standard atmosphere and inspect surfaces for contamination or defects
- Calibrate and zero the hazemeter using reference standards traceable to national metrology institutes
- Measure at least three to five specimens per sample, or multiple positions on large sheets, and report individual and mean values
- Record specimen thickness, since haze generally increases with thickness due to bulk scattering
- Round and report haze values, typically to the nearest 0.1 percentage point
Key factors that influence haze results include material crystallinity, additive content such as antiblock and slip agents, pigment and filler loading, molecular orientation, surface roughness, thickness, and processing conditions. Accredited third-party laboratories control these variables through standardized specimen preparation and conditioning to ensure reproducible, comparable results.
Applications
Haze index testing supports quality control, material qualification, and product development across many industries:
- Food and beverage packaging: transparency requirements for films, bottles, and containers where product visibility is a purchasing factor
- Agricultural films: greenhouse and mulch films where diffuse light transmission influences crop growth
- Lighting engineering: LED diffusers, lamp covers, and light guide panels designed with intentionally controlled or elevated haze for uniform illumination
- Display and electronics: touch panel covers, display windows, and optical films requiring low haze for image sharpness
- Automotive and transportation: headlamp lenses, instrument covers, and transparent glazing components with strict optical clarity specifications
- Construction: polycarbonate and PMMA glazing sheets, roofing panels, and skylights balancing light transmission with diffusion
- Medical and consumer products: transparent containers, device windows, and packaging requiring verified optical performance
Typical acceptance criteria vary by application: high-clarity optical films may require haze below 2%, general packaging films commonly fall in the 2–8% range, while lighting diffuser products may deliberately specify haze values above 40% to achieve uniform soft light output.
FAQ
What is the difference between haze and transmittance?
Transmittance measures how much light passes through a specimen in total, while haze measures the fraction of that transmitted light that is scattered away from the straight-through direction. A material can have high transmittance and high haze (a bright but cloudy appearance) or high transmittance and low haze (a genuinely clear appearance).
How is haze different from clarity?
Haze quantifies wide-angle light scattering that causes a milky or washed-out appearance. Clarity, sometimes called see-through quality, describes the ability to perceive fine detail through a material and is governed by narrow-angle scattering. Thin films with low haze can still show poor clarity due to distortion effects.
Does specimen thickness affect the haze result?
Yes. Haze arises from both surface scattering and bulk scattering, and the bulk contribution increases with thickness. Haze values are only comparable between specimens of identical thickness, which is why thickness must always be reported together with the haze result.
Which standard should be selected for testing?
ASTM D1003 and GB/T 2410 are widely used in North America and China respectively, while ISO 14782 and JIS K 7136 are common in international and Japanese supply chains. The standards are technically aligned in principle, but the choice should follow the specification referenced by the customer or product standard.
Can colored, tinted, or translucent materials be tested?
Yes, provided sufficient light is transmitted. Highly opaque materials cannot be characterized for haze since the measurement requires measurable transmitted flux. For colored materials, the spectrophotometer method with the correct illuminant and observer settings is recommended.
How many specimens should be tested?
Best practice is to test a minimum of three to five specimens, or several locations on large sheets, and report both individual and mean values, because surface defects and thickness variation can produce meaningful scatter in the results.