Haze measurement is a critical quality control test for evaluating the optical clarity of transparent and translucent plastic materials such as films, sheets, and molded parts. This article explains the standardized plastic haze measurement methods based on ASTM D1003, ISO 14782, and GB/T 2410, covering testing principles, sample preparation, calculation formulas, and practical applications across packaging, automotive, and display industries.
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. In other words, haze quantifies wide-angle light scattering within or at the surface of a material, which causes a cloudy or milky appearance and reduces the ability to see objects clearly through the specimen. Haze is distinct from total luminous transmittance, which measures the overall amount of light that passes through the material regardless of scattering angle.
For transparent plastics, haze is one of the most important optical performance indicators. Low-haze materials are required for display covers, optical lenses, and premium packaging, while controlled high-haze materials are deliberately engineered for lighting diffusers and agricultural films. The measurement of haze is governed by several internationally recognized standards, including ASTM D1003 (Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics), ISO 14782 (Plastics — Determination of Haze for Transparent Materials), and the Chinese national standard GB/T 2410. Japanese Industrial Standard JIS K 7361 also addresses luminous transmittance measurement for plastics.
Light scattering in plastics originates from two principal sources: surface scattering caused by roughness, scratches, abrasion, or matte textures, and internal scattering caused by crystallinity, fillers, pigments, phase separation, gels, or voids within the polymer matrix. Because haze depends strongly on specimen thickness and surface condition, these parameters must always be reported together with the measured haze value.
Testing Samples
Films and Flexible Sheets
Plastic films used in packaging, agriculture, and electronics protection are the most common specimens for haze testing. Films should be flat, free of wrinkles and visible defects, and cut to the dimensions required by the specimen holder. Both single-layer and multilayer (laminated) films can be tested, and the total thickness must be recorded.
Rigid Sheets and Injection-Molded Plaques
Transparent sheets such as PET, PMMA (acrylic), PC (polycarbonate), and PVC can be tested directly after cutting to size. For materials supplied as granules or pellets, test plaques should first be produced by compression molding or injection molding under controlled conditions to ensure representative and reproducible specimens.
Sample Dimensions and Conditioning
ASTM D1003 recommends specimens of approximately 50 mm (2 inches) in diameter or 50 mm × 50 mm squares, with the thickness as agreed upon between parties. Similar dimensions are specified in GB/T 2410. At least three specimens per material are recommended, and results are typically averaged. Prior to testing, specimens should be conditioned in a standard laboratory atmosphere of 23 ± 2 °C and 50 ± 5% relative humidity in accordance with ISO 291 or ASTM D618 to stabilize their optical and dimensional properties.
Testing Items
A complete optical characterization of transparent plastics typically includes the following measurable quantities:
- Haze (percent): the fraction of transmitted light scattered more than 2.5 degrees from the incident beam direction.
- Total luminous transmittance (percent): the ratio of transmitted light to incident light over the visible spectrum.
- Diffuse transmittance (percent): the portion of transmitted light that is scattered rather than transmitted directly.
- Specular transmittance (optional): the light transmitted within 2.5 degrees of the geometric direction, used to derive clarity-related evaluations.
- Surface and thickness characterization: specimen thickness, surface texture, and conditioning history documented alongside the optical values.
Testing Methods
Principle of Measurement
Both ASTM D1003 and ISO 14782 employ an integrating sphere photometer or a dedicated hazemeter operating on a unidirectional illumination, diffuse-viewing geometry (0/d). A collimated beam of light passes through the specimen mounted against the entry port of an integrating sphere. A light trap (or an optical switch in automated instruments) selectively removes the specular component so that only scattered light is collected, allowing separation of total and diffuse transmittance. ASTM D1003 traditionally specifies CIE Illuminant C with the 2-degree standard observer, while also permitting D65; ISO 14782 specifies D65 illumination.
Method A — Hazemeter (Automatic Instrument)
In the automated hazemeter method, the instrument performs the required optical switching internally and directly calculates haze and total transmittance after calibration. Certified haze reference standards, typically with nominal values such as approximately 1%, 5%, 10%, and 25%, are used to verify instrument performance before testing. This method offers high repeatability and is preferred for routine quality control in accredited third-party laboratories and production environments.
Method B — Spectrophotometer (Four-Reading Procedure)
The classical four-reading procedure, historically performed with a spectrophotometer fitted with an integrating sphere, remains the reference approach. The four measurements are defined as follows:
- T1: incident light reading with no specimen, sphere in baseline configuration.
- T2: total transmitted light reading with the specimen in place.
- T3: instrument scatter reading with the light trap engaged and no specimen.
- T4: scatter reading with the specimen in place and the trap engaged.
The results are calculated using the following expressions:
- Total luminous transmittance: Tt = (T2 / T1) × 100
- Diffuse transmittance: Td = [(T4 − T3) / T1] × 100
- Haze = (Td / Tt) × 100 = [(T4 − T3) / T2] × 100
All values are expressed as percentages. Specimens must be clean, fingerprint-free, and mounted without bending, since surface contamination and stress can artificially inflate haze readings.
Factors Affecting Results
- Specimen thickness: haze generally increases with thickness, so comparisons are only valid at equal thickness.
- Surface condition: scratches, dust, embossing, and matte finishes dramatically increase surface scattering.
- Material structure: crystallinity in PP or PET, filler content, and phase-separated additives raise internal scattering.
- Instrument calibration and geometry: regular verification against traceable haze standards is essential for interlaboratory agreement.
Applications
Haze measurement supports material development, incoming inspection, and final product release across many industries:
- Flexible and rigid packaging: verifying the clarity of PE, PP, PET, and PVC films and containers so that packaged products remain visually appealing on the shelf.
- Display and electronics: confirming that protective films, touch panel covers, and optical adhesives meet low-haze specifications, frequently below 1–2 percent for high-end components.
- Automotive: evaluating instrument cluster covers, headlamp lenses, window glazing, and interior trim for compliance with optical quality requirements.
- Lighting: characterizing light-diffusing PC and PMMA panels, where high, uniform haze is intentionally achieved to eliminate glare and hot spots.
- Agriculture: assessing greenhouse and mulch films, where a balance between direct transmittance and diffuse light scattering influences crop growth.
- Medical devices: validating the transparency of blister packs, IV containers, and diagnostic consumibles for content visibility.
- Research and development: comparing resin formulations, processing parameters, and additive packages during optical-grade material development.
FAQ
What is the difference between haze and transmittance?
Transmittance measures how much light passes through a specimen in total, while haze measures only the portion of transmitted light that is scattered by more than 2.5 degrees. A material can have high transmittance yet high haze, appearing bright but cloudy.
Which standard should be selected: ASTM D1003 or ISO 14782?
The choice usually follows the specification referenced by the customer, the end market, or the product standard. The two methods are conceptually equivalent, but they differ in specified illuminant and minor procedural details, so results should not be assumed interchangeable without correlation data.
How many specimens are required?
At least three representative specimens are commonly tested, with the average haze and transmittance reported along with specimen thickness and conditioning conditions.
Can translucent, textured, or colored materials be tested?
Translucent materials can be tested, but the physical meaning of haze becomes less straightforward as transmittance decreases, and highly opaque materials are unsuitable. Textured or embossed surfaces can be measured, but the surface condition must be clearly documented because surface scattering dominates the result.
What haze values are typical for common plastics?
Optical-grade PMMA and PC sheets often show haze below 0.5–1 percent. Clarified polypropylene films typically fall in the range of a few percent, while standard polyethylene films may range from about 5 to 20 percent depending on formulation and thickness. Acceptance limits are always defined by the applicable product specification.
Why must thickness be reported with haze results?
Because scattering occurs throughout the bulk of the material, haze increases roughly with thickness. Reporting thickness ensures that results from different sources or material grades can be compared meaningfully.