Plastic Haze Test Methods: Standards, Procedures, and Applications

Haze testing is a critical optical measurement used to evaluate the light-scattering behavior of transparent and translucent plastic materials such as films, sheets, and molded parts. This technical article explains the principles of plastic haze testing, the major international standards such as ASTM D1003, ISO 14782, and GB/T 2410, sample requirements, test procedures, calculation methods, and typical industrial applications.

Technical Overview

Haze is defined as the percentage of transmitted light that, in passing through a specimen, deviates from the incident beam by more than 2.5 degrees through forward scattering. In plastic materials, haze is caused by wide-angle light scattering from surface roughness, bulk crystallinity, filler particles, voids, additives, and processing defects. High haze produces a milky or cloudy appearance and reduces the sharpness of objects viewed through the material.

Haze should not be confused with total luminous transmittance. Transmittance measures the total amount of light that passes through a specimen, while haze measures only the scattered portion of that transmitted light. A material can exhibit high transmittance and high haze at the same time, which is typical of lighting diffusers, or high transmittance with very low haze, which is required for optical glazing and display covers. A third related property, clarity, refers to small-angle scattering below 1.5 degrees and governs the fine detail resolution visible through a specimen, but it is measured separately from haze.

Because haze directly affects the visual quality and end-use performance of transparent plastics, it is a routine quality control parameter in film extrusion, sheet production, injection molding, and optical component manufacturing. Quantitative haze measurement requires a dedicated hazemeter or a spectrophotometer equipped with an integrating sphere operated under standardized geometry.

Testing Samples

Flexible Films

Packaging and industrial films made from polyethylene (PE), polypropylene (PP), biaxially oriented polypropylene (BOPP), polyethylene terephthalate (PET), and multilayer laminates are the most frequently tested sample type. Films are usually tested at their nominal production thickness, and at least three to five specimens should be cut from different positions across the web width to account for gauge variation.

Rigid Sheets and Panels

Flat specimens of polymethyl methacrylate (PMMA), polycarbonate (PC), rigid PVC, polystyrene (PS), and glass-reinforced transparent composites can be tested directly, provided the surfaces are clean and free of scratches. Thick or textured specimens require special attention because surface texture contributes strongly to measured haze.

Molded and Formed Parts

Injection-molded lenses, lighting covers, appliance windows, and thermoformed components may be tested if a sufficiently flat area of appropriate size can be presented to the specimen port. Curved or non-flat parts are generally tested by cutting flat sections from representative regions of the part.

Sample Preparation Requirements

• Specimen size must fully cover the instrument port, typically 50 mm by 50 mm or a disc of at least 45 mm in diameter, depending on the apparatus.
• Surfaces must be free of fingerprints, dust, oils, and scratches, since contamination artificially increases haze readings.
• Specimens should be conditioned at 23 ± 2 °C and 50 ± 10% relative humidity for a minimum of 40 hours prior to testing, unless otherwise specified.
• Report the nominal thickness of each specimen, because haze increases with thickness in scattering materials and comparison is only valid at equal thickness.
• Avoid bending, stretching, or stressing film specimens during handling and mounting, as stress-induced birefringence and deformation can alter results.

Testing Items

A standard haze test report for plastic materials typically includes the following measured and calculated quantities:

• Haze (H): the percentage of transmitted light scattered more than 2.5 degrees from the incident beam, reported to the nearest 0.1%.
• Total luminous transmittance (Tt): the ratio of total transmitted light to incident light, expressed as a percentage.
• Diffuse transmittance (Tdiffuse): the scattered component of transmission, from which haze is derived.
• Specimen identification: material designation, thickness, surface condition, and number of specimens tested.
• Statistical results: mean value, standard deviation, and the range observed across all specimens.

Testing Methods

Applicable Standards

• ASTM D1003: the most widely used method for haze and luminous transmittance of transparent plastics. Method A uses a hazemeter, and Method B uses an integrating-sphere spectrophotometer. It defines haze with a scattering limit of 2.5 degrees.
• ISO 14782: the international standard for haze determination of transparent materials, technically equivalent to ASTM D1003 in principle and geometry.
• GB/T 2410: the Chinese national standard for haze and transmittance of transparent plastics, harmonized with ASTM D1003 and widely applied in the Chinese plastics industry.
• JIS K 7361-1: the Japanese standard specifying total luminous transmittance measurement using an integrating sphere, commonly paired with haze determination.
• JIS K 7136: the Japanese standard for haze of transparent plastics, corresponding to ISO 14782.

Test Apparatus

The measurement is performed with either a dedicated hazemeter or a double-beam spectrophotometer fitted with an integrating sphere. The light source, typically illuminant A, C, or D65 with a defined photopic response, directs a parallel beam through the specimen mounted at the sphere port. A light trap or opacity absorber located opposite the entry port allows the scattered component of transmitted light to be collected by the highly reflective sphere wall while the specular component is excluded. Reference calibration is performed using a certified haze standard and a fully open beam reading.

Test Procedure

• Step 1: Warm up and calibrate the instrument following the manufacturer procedure, verifying zero transmission and full-scale readings with certified haze and transmittance reference standards.
• Step 2: Measure the incident light flux T1 with no specimen in place and the light trap open to the sphere.
• Step 3: Place the specimen at the transmission port and measure the total transmitted flux T2 with the light trap closed so that both specular and diffuse light are collected.
• Step 4: Remove the specimen and, with the light trap positioned to exclude the specular beam, measure the instrumental scattered flux T3.
• Step 5: Replace the specimen and, with the light trap still excluding the specular beam, measure the combined specimen and instrument scattered flux T4.
• Step 6: Calculate haze and transmittance using the standard equations and report the average of all valid specimens.

Calculation Formulas

Total luminous transmittance is calculated as Tt = (T2 / T1) × 100. Haze is calculated as H = [(T4 / T2) − (T3 / T1)] × 100, where the subtraction of the T3/T1 term compensates for the inherent scatter contribution of the instrument itself. Both quantities are expressed as percentages. For materials with a transmittance below approximately 30%, haze values lose practical significance and should be interpreted with caution, as specified in ASTM D1003.

Factors Affecting Results

• Specimen thickness: thicker specimens scatter more light and show higher haze, so thickness must always be reported alongside the result.
• Surface texture: matte, embossed, or micro-structured surfaces dramatically increase measured haze relative to polished surfaces.
• Internal morphology: crystallinity, spherulite size, pigment dispersion, and voids contribute to bulk scattering.
• Temperature and conditioning history: moisture absorption and thermal history can change light scattering behavior in hygroscopic polymers.
• Instrument condition: dust on optics, sphere wall contamination, and uncalibrated light traps introduce systematic bias.

Applications

Haze test data on plastic materials support a broad range of industrial uses:

• Flexible packaging: verifying that BOPP, PET, and PE films meet haze and gloss specifications for print clarity and product visibility on retail shelves.
• Rigid packaging: qualifying transparent containers, thermoformed trays, and blister films for optical appearance requirements.
• Lighting industry: controlling the haze level of PMMA and PC diffuser sheets to achieve the required balance between light distribution and transmission efficiency.
• Automotive and transportation: evaluating transparent PC glazing, instrument panel covers, and headlamp lenses against optical quality limits.
• Consumer electronics: incoming inspection of protective films, display windows, and touch panel substrates where low haze is essential.
• Construction: classification of transparent and translucent roofing, greenhouse films, and architectural glazing panels by light-diffusion performance.
• Research and development: comparing resin formulations, nucleating agents, processing conditions, and surface treatments during new material development.
• Regulatory compliance: demonstrating conformity to product specifications, purchase agreements, and certification requirements through accredited third-party laboratories.

FAQ

What is haze in plastic materials?

Haze is the percentage of transmitted light that is scattered by more than 2.5 degrees from the direction of the incident beam. It quantifies the cloudy or milky appearance of a transparent plastic caused by surface and internal light scattering.

Which standard should I choose: ASTM D1003, ISO 14782, or GB/T 2410?

All three standards share the same basic principle, apparatus geometry, and calculation method. ASTM D1003 is common in North American supply chains, ISO 14782 is preferred for international trade, and GB/T 2410 is the established Chinese national standard. When results are compared across standards, differences in illuminant, specimen conditioning, and reporting details should be verified.

What is the difference between haze and transmittance?

Transmittance measures the total fraction of incident light passing through the specimen, while haze measures only the scattered portion of that transmitted light. A lighting diffuser may combine 85% transmittance with 90% haze, whereas an optical-grade sheet may show 92% transmittance with haze below 0.5%.

Does specimen thickness affect the haze result?

Yes. Haze generally increases with thickness because scattering occurs throughout the bulk of the material. Haze values are only comparable between specimens of the same nominal thickness, which is why thickness must always be reported with the test result.

How many specimens should be tested?

Most standards recommend testing at least three specimens per sample, and five or more for film products with known variability. The reported result is the arithmetic mean, together with the observed range or standard deviation.

Can colored or translucent materials be tested for haze?

Materials must transmit enough light for a valid measurement. ASTM D1003 cautions that haze readings on specimens with total transmittance below about 30% are of limited practical significance. Highly pigmented or opaque plastics are not suitable for this test.

How should specimens be cleaned before testing?

Use a soft lint-free cloth with a mild cleaning agent such as diluted isopropanol if permitted by the material, allow full evaporation before measurement, and always handle specimens by the edges to avoid fingerprints on the optical surfaces.