Gloss Measurement of Packaging Materials: Standards, Methods, and Applications

Gloss measurement of packaging materials is a critical surface-quality test that quantifies the specular reflectance of films, paperboard, printed surfaces, and coated laminates using standardized geometries such as 20°, 60°, 75°, and 85°. This technical article explains the measurement principles, applicable international standards including ISO 2813, ISO 8254, ASTM D523, ASTM D2457, TAPPI T480, and GB/T 8941, sample preparation, testing procedures, and practical applications in packaging quality control.

Technical Overview

Gloss is an optical attribute of a surface that describes its capacity to reflect light specularly, that is, in a mirror-like direction. On packaging materials, gloss directly influences visual perception, shelf appeal, print fidelity, and the perceived quality of the finished product. Gloss is not an intrinsic material constant; it depends on surface smoothness, refractive index, coating thickness, calendering degree, and the angle of illumination and observation.

In instrumental terms, gloss is quantified with a glossmeter (reflectometer), which projects a beam of light onto the surface at a defined incidence angle and measures the intensity of light reflected at the specular angle. The result is expressed in gloss units (GU), calculated as the ratio of the reflectance of the specimen to that of a polished black glass reference standard of defined refractive index, multiplied by 100. Commonly used measurement geometries include 20°, 45°, 60°, 75°, and 85°, each suited to a specific gloss range and material class:

• 20° geometry – designed for high-gloss surfaces such as cast polypropylene films, UV-varnished printed cartons, and metallized laminates.
• 60° geometry – the general-purpose geometry covering low, medium, and high gloss ranges for most packaging surfaces.
• 75° geometry – historically developed for paper and paperboard, particularly coated printing grades, and widely used in the pulp and paper segment.
• 85° geometry – intended for matte or low-gloss surfaces such as uncoated board, textured papers, and anti-glare films.
• 45° geometry – applied to plastic films and certain ceramics per North American test methods.

Principal reference standards include ISO 2813 and ASTM D523 for paints, coatings, and non-metallic surfaces at 20°, 60°, and 85°; DIN 67530 as the equivalent reflectometric method; ISO 8254 (Parts 1 and 2) for 75° specular gloss of paper and board; TAPPI T480 for 75° paper gloss; ASTM D2457 for specular gloss of plastic films and solid plastics; and the Chinese national standards GB/T 9754 for paint films and GB/T 8941 for paper and paperboard at 20°, 60°, and 75°. Testing is routinely performed by manufacturers, converters, and accredited third-party laboratories to verify appearance consistency and specification compliance.

Testing Samples

Flexible Plastic Films

Biaxially oriented polypropylene (BOPP), polyester (PET), polyethylene (PE), polyamide (PA), PVC, and cellophane films, either plain, printed, corona-treated, or lacquered. Transparent films should be measured over a standardized black backing to eliminate the influence of transmitted light and underlying surfaces.

Metallized and Barrier Laminates

Vacuum-metallized aluminum films, foil laminates, and barrier structures used for pouches, coffee packaging, and blister foils. These substrates typically exhibit high gloss values and are evaluated at 20° or 60° geometry.

Paper and Paperboard

Coated art paper, cast-coated paper, folding boxboard, white-lined chipboard, kraft paper, and label papers. For these materials, surface smoothness, coating formulation, and calendering intensity are the dominant gloss determinants, and the 75° geometry is most representative.

Printed and Converted Surfaces

Lithographic, flexographic, gravure, and digitally printed packaging surfaces, including UV-cured or water-based varnish coatings, laminated glossy or matte finishes, soft-touch coatings, and hot-stamping foil decorations.

Rigid Packaging Components

Injection-molded or thermoformed containers, closures, cosmetic jars, tubes, and rigid boxes, where mold polish and surface texture control the resulting gloss level.

Testing Items

Typical gloss determination services for packaging materials cover the following measurands:

• Specular gloss at 20° for high-gloss films, varnished prints, and metallized surfaces (GU, typically up to 2000 GU on some reflectance scales but commonly reported within 0–200 GU).
• Specular gloss at 60° as the universal screening geometry for nearly all packaging substrates.
• Specular gloss at 85° for matte and low-gloss surfaces such as uncoated and textured boards.
• Specular gloss at 75° for paper and paperboard per ISO 8254 and TAPPI T480.
• Specular gloss at 45° for plastic films per ASTM D2457.
• Gloss uniformity and mottle assessment – multiple-point measurements across the web or sheet to quantify variation and directional anisotropy.
• Gloss retention – measurement before and after abrasion, rub testing, humidity exposure, or accelerated aging to evaluate durability of the finish.

Testing Methods

Instrumentation and Calibration

A calibrated glossmeter conforming to the geometry, spectral response, and tolerance requirements of the applicable standard is used. Calibration is performed against a primary highly polished black glass standard with a refractive index of 1.567, which by definition assigns a value of approximately 100 GU for each geometry. A working tile of known gloss value is measured immediately before testing, and instrument drift is verified after the measurement sequence. Modern instruments offer single-angle or triple-angle (20°/60°/85°) configurations with automated diagnostics.

Sample Preparation and Conditioning

• Specimens shall be flat, clean, and free of fingerprints, dust, creases, and surface defects; the test area must be at least as large as the instrument aperture.
• Flexible films are flattened and, when transparent, mounted on a black opaque backing.
• Conditioning is carried out at 23 ± 2 °C and 50 ± 5 % relative humidity in accordance with ISO 187 for paper and board or ISO 291 for plastics prior to measurement.
• For anisotropic or machine-directional surfaces, measurements are taken in both machine direction (MD) and cross direction (CD), and the orientation is reported.

Measurement Procedure

The specimen is placed on a flat, rigid support and the glossmeter is lowered onto the surface without gaps or tilt. The standard practice begins at 60°: if the reading exceeds approximately 70 GU, the measurement is repeated at 20°; if the reading falls below approximately 10 GU, the 85° geometry is used instead. At least three to ten readings are taken at different locations on each specimen, and the arithmetic mean, standard deviation, and measurement geometry are reported. Results are expressed in gloss units (GU) together with the test standard, specimen orientation, and, for transparent films, details of the backing.

Key Influence Factors

• Surface roughness and micro-texture, which scatter light and reduce specular reflectance.
• Refractive index of the coating or substrate layer at the surface.
• Coat weight, varnish film thickness, and degree of cure of printed coatings.
• Calendering pressure and coating formulation for paperboard.
• Sample curvature, waviness, and poor contact with the instrument aperture.

Applications

Gloss determination on packaging materials supports a broad range of industrial and commercial objectives:

• Incoming material inspection – verifying that purchased films, foils, and boards meet contractual gloss specifications before conversion.
• Process control in printing and converting – optimizing varnish application, UV lamp power, laminating pressure, and calendering settings.
• Batch-to-batch consistency – ensuring uniform appearance across production runs and between different suppliers or plants.
• Brand and artwork approval – validating that matte, satin, or high-gloss finishes match approved proofs and brand appearance standards.
• Competitive benchmarking – quantifying surface appearance against reference materials in product development.
• Failure and complaint analysis – diagnosing gloss loss, blooming, blocking, or coating defects in returned goods.
• Research and development – correlating gloss with coating chemistry, surface roughness profilometry, and printability studies.

Typical reporting industries include flexible packaging, folding cartons, labels and shrink sleeves, tobacco and beverage packaging, cosmetics packaging, pharmaceutical blister materials, and metal container coatings.

FAQ

What is a gloss unit (GU)?

A gloss unit is the relative measure of specular reflectance compared with a polished black glass standard that has a refractive index of 1.567 and is assigned a value of approximately 100 GU. A perfect mirror reads about 1000 GU, while matte surfaces may read below 5 GU.

Which measurement angle should be selected?

The 60° geometry serves as the universal starting point. High-gloss surfaces above about 70 GU at 60° are better differentiated at 20°, while matte surfaces below about 10 GU are better characterized at 85°. Paper and board are conventionally measured at 75°, and plastic films may be assessed at 45° or 20° depending on the applicable standard.

What is the difference between gloss and haze?

Gloss measures light reflected at the mirror angle, whereas haze (reflectance haze) quantifies light scattered near the specular direction. A surface can show an acceptable gloss value yet appear milky or tarnished due to high haze, so both parameters are often evaluated together for high-end finishes.

Can curved or flexible packaging be measured?

Conventional glossmeters require a flat contact area. Cans, bottles, and tubes demand special fixtures, localized apertures, or benchtop instruments adapted to curved geometry, and results should be interpreted with the geometry limitation clearly stated in the report.

How are results reported and what tolerances are typical?

Results are reported as the mean gloss value in GU together with the measurement geometry, standard applied, number of readings, and standard deviation. Commercial tolerances are typically agreed between buyer and supplier; a common criterion for visual equivalence is a difference of no more than about 3–5 GU on medium-gloss surfaces.

How often should a glossmeter be calibrated?

The instrument should be verified against its calibrated working standard before each measurement session, and full traceable recalibration should be performed at the interval recommended by the manufacturer, commonly every twelve months, through an accredited calibration laboratory.