Color Fastness Testing for Plastic Flooring: Standards, Methods and Assessment

Color fastness testing evaluates the ability of plastic flooring (PVC/vinyl flooring, resilient floor coverings) to retain its color when exposed to light, heat, rubbing, and other service conditions. This article explains the testing principle, applicable standards such as the ISO 105 series, ASTM F1514 and F1515, GB/T and JIS methods, sample requirements, test procedures, and grading criteria commonly applied by accredited third-party laboratories. It is intended as a practical technical reference for flooring manufacturers, quality engineers, and building material specifiers.

Technical Overview

Color fastness is the resistance of a material's color to change under specified environmental and mechanical stresses, or its resistance to transferring color to adjacent surfaces. For plastic flooring, including PVC sheet, vinyl tile, and rigid-core products, color fastness is a key durability indicator because the visual appearance of the floor must remain stable over years of exposure to sunlight through windows, artificial lighting, heat, foot traffic, and cleaning processes.

The main mechanisms that affect the color of plastic flooring include ultraviolet degradation of pigments and polymers, thermal yellowing of the wear layer and PVC binder, plasticizer migration, surface abrasion, and staining from contact with other materials. A comprehensive color fastness evaluation therefore addresses several stress types rather than a single exposure condition.

Results are expressed using two widely accepted grading systems. The grey scale (ISO 105-A02 for change in color, ISO 105-A03 for staining) grades performance from 1 (severe change or staining) to 5 (no visible change or staining), with intermediate half-steps. For light fastness specifically, the blue wool reference scale grades performance from 1 (very poor) to 8 (outstanding), where each step represents approximately a doubling of exposure resistance.

• Relevant international standards: ISO 105-B02, ISO 105-B04, ISO 105-X12, ISO 105-A02/A03, ISO 105-J03
• Relevant American standards: ASTM F1515 (light stability), ASTM F1514 (thermal color stability), ASTM D2244 (instrumental color difference)
• Relevant Chinese standards: GB/T 8427, GB/T 3920, GB/T 250, GB/T 251, and the PVC flooring product standard GB/T 11982
• Relevant Japanese standards: JIS A 5705 (vinyl flooring sheets and tiles) with JIS L 0842 for xenon arc light fastness

Testing Samples

Homogeneous PVC Sheet Flooring

Homogeneous flooring has a single-layer composition in which color pigment is distributed throughout the full thickness. Fading or discoloration affects the entire body of the material, so light fastness and thermal stability testing are the primary concerns for this sample type.

Heterogeneous Vinyl and Luxury Vinyl Tile (LVT)

Heterogeneous products and LVT rely on printed decor layers protected by transparent wear layers. Because the visual pattern is concentrated in a thin printed film, these samples are evaluated for light fastness of the printed ink system, yellowing of the wear layer, and migration or staining at product edges.

Rigid Core Flooring (SPC and WPC)

Stone plastic composite (SPC) and wood plastic composite (WPC) flooring combine a rigid core with printed decor and overlay layers. Color fastness testing verifies that the decor layer, embossed surface, and UV coating maintain their original appearance after light and thermal exposure.

Specimen Preparation and Conditioning

Test specimens are cut from production samples or finished products, typically in sizes such as 100 mm x 50 mm or sufficient to cover the exposure aperture of the test apparatus, together with an unexposed control specimen retained for comparison. Before testing, specimens are conditioned in a standard atmosphere in accordance with ISO 291 (23 ± 2 °C and 50 ± 5 % relative humidity) for a defined period, usually at least 24 hours, to ensure reproducible results.

Testing Items

Depending on the product type, target market, and specification requirements, a color fastness evaluation program for plastic flooring typically includes the following items:

• Color fastness to artificial light (xenon arc): resistance to fading under simulated sunlight
• Color fastness to light and weathering (light plus water spray): for floors exposed to direct sunlight or semi-outdoor conditions
• Thermal color stability: resistance to heat-induced discoloration and yellowing
• Color fastness to rubbing (dry and wet crocking): transfer of color to a rubbing cloth under dry and wet conditions
• Staining and color migration: color transfer to or from adjacent materials and surfaces
• Color difference after aging: instrumental determination of total color difference (ΔE) between exposed and unexposed specimens

Testing Methods

Light Fastness Test (Xenon Arc Exposure)

The xenon arc test is performed in accordance with ISO 105-B02 (also adopted as EN ISO 105-B02, GB/T 8427, and JIS L 0842). A filtered xenon arc lamp simulates daylight, and the specimen is exposed alongside a set of blue wool references under controlled chamber temperature and humidity. Exposure continues until the blue wool references reach the specified contrast change, after which the specimen is compared with the references and assigned a light fastness grade from 1 to 8. For resilient floor coverings specifically, ASTM F1515 describes xenon arc exposure of flooring specimens with evaluation of color change by grey scale or by instrument. Product specifications and certification schemes for commercial flooring commonly require a minimum light fastness equivalent to blue wool grade 6 or higher.

Thermal Color Stability Test

Thermal color stability is evaluated following ASTM F1514, in which vinyl flooring specimens are exposed to an elevated temperature in a ventilated oven for a defined duration. After cooling and conditioning, the exposed specimens are compared with unexposed controls using the grey scale for change in color (ISO 105-A02 / GB/T 250) or by instrumental color measurement. This test detects heat-induced yellowing, whitening, or pigment shift that may occur during transport, storage, or installation near heat sources, and it is particularly relevant for white and pastel shades.

Rubbing Color Fastness Test (Crocking)

Rubbing color fastness is determined using a crockmeter in accordance with ISO 105-X12 or GB/T 3920. A standard white cotton rubbing cloth, either dry or pre-wetted, is rubbed against the flooring surface under a defined downward force for a specified number of strokes. The degree of color transfer onto the cloth is assessed with the grey scale for staining (ISO 105-A03 / GB/T 251), with grade 5 indicating no staining. Dry and wet rubbing grades are reported separately, since wet conditions can accelerate pigment and plasticizer transfer.

Instrumental Color Difference Measurement

For objective and repeatable assessment, color change is measured with a spectrophotometer or colorimeter using the CIELAB color space, typically under the D65 illuminant with the 10-degree standard observer. The total color difference (ΔE) between exposed and unexposed areas is calculated according to ISO 105-J03 or ASTM D2244. Many specifications define pass/fail limits, for example maximum ΔE values of 1.0 to 3.0 depending on product class and application, which reduces subjectivity compared with visual grading alone.

Assessment and Grading Criteria

Visual assessment is performed by trained evaluators under standardized lighting, using calibrated grey scales for change in color and for staining. For light fastness, the blue wool comparison method remains the reference approach. When both visual and instrumental results are obtained, they are reported together to give a complete picture of performance, and any borderline results are confirmed with replicate specimens.

Applications

Color fastness testing supports quality control, product development, and market access across the entire plastic flooring supply chain. Typical applications include:

• Incoming quality control of pigments, masterbatches, printed decor films, and UV stabilizers before mass production
• Verification of production consistency between batches and production lines
• Compliance demonstration for product standards and certification schemes in European, American, Chinese, and Japanese markets
• Formulation development and comparison of UV absorbers, light stabilizers, and wear layer recipes
• Project specification and acceptance for sunlit interiors such as airport terminals, shopping mall atriums, hospitals, schools, and exhibition halls
• Warranty support and failure analysis when fading, yellowing, or staining disputes arise after installation

Manufacturers exporting to multiple regions often consolidate testing with accredited third-party laboratories so that one specimen set can be evaluated against ISO, EN, ASTM, GB/T, and JIS requirements simultaneously, shortening time to market.

FAQ

What light fastness grade is generally required for plastic flooring?

Requirements vary by product standard and application, but commercial flooring specifications typically demand a minimum of blue wool grade 6, while premium or heavily sun-exposed installations may require grade 7 or 8. On the grey scale, a change in color of grade 4 or better after the specified exposure is a common acceptance criterion. Always confirm the exact limit with the applicable product standard or project specification.

What is the difference between the grey scale and the blue wool scale?

The grey scale (grades 1 to 5) measures the magnitude of visible color change or staining of a specimen and is used for general color fastness assessments. The blue wool scale (grades 1 to 8) is specific to light fastness and expresses how long a material resists fading, with each step representing roughly double the exposure time of the previous step. A higher number always indicates better performance on both scales.

How long does xenon arc light fastness testing take?

The exposure duration is not fixed by time but by the behavior of the blue wool references: exposure continues until the required reference shows the defined contrast change. In practice, runs range from roughly 24 hours for lower grades to more than 100 chamber hours for high-performance products rated blue wool 7 or 8, after which evaluation and reporting add a few working days.

Why is thermal color stability tested separately from light fastness?

Heat alone can cause yellowing or pigment changes without any UV involvement, for example during hot storage in containers or underfloor heating conditions. ASTM F1514 isolates the thermal effect so that formulations can be optimized for heat stability independently of their light stabilizer package.

Can instrumental ΔE measurement replace visual grey scale grading?

Instrumental measurement provides objective, repeatable ΔE values and is increasingly specified as the acceptance criterion, but visual grading with calibrated grey scales remains the reference method in most color fastness standards. The best practice is to report both: instrument data for precision and traceability, and visual grades for direct comparison with historical specifications and buyer requirements.