Overview
EN ISO 12625-16:2024 (ISO 12625-16:2024) is the CEN-endorsed European standard for measuring the opacity of tissue paper and tissue products using the diffuse reflectance method with a paper backing. The document specifies instrumental procedures, conditioning and sampling requirements, and sample preparation for both single‑ply and multi‑ply products. It clarifies that the method measures the degree to which a sheet visually obscures print on underlying sheets (opacity), distinct from transparency or translucency.
Key topics and technical requirements
- Principle: Opacity is determined from luminance‑factor (diffuse reflectance) measurements under defined spectral and geometric conditions.
- Apparatus: Use of a calibrated reflectometer and suitable reference and working standards; provision for a black cavity for certain measurements.
- Spectral control: For products with fluorescent whitening agents (FWAs), the UV content of incident radiation must be adjusted to match CIE illuminant C using a fluorescent reference standard as described in ISO 2470‑1.
- Sampling and conditioning: References ISO 186 and ISO 187 for representative sampling and standard atmosphere conditioning before testing.
- Preparation of test pieces: Specific instructions for preparing single‑ply and multi‑ply samples where special handling is required.
- Procedure, calculation and reporting: Defined measurement procedure, equations for calculating opacity from luminance‑factor data, and required test report items.
- Instrument specifics: Annex A covers spectral characteristics and added guidance for instruments with bandpass correction (including weighting functions). Annex B gives precision information.
Practical applications and users
- Quality control and R&D in tissue paper manufacturing - to monitor and specify product appearance and opacity performance.
- Independent testing laboratories and accredited facilities performing instrument-based optical property testing.
- Suppliers and brand owners who need to specify or verify opacity for consumer products (e.g., toilet paper, facial tissue, napkins).
- Regulatory bodies and procurement requiring standardized optical testing methods for tendering or compliance.
- Useful for evaluating effects of fillers, fiber composition and fluorescent whitening agents on perceived opacity.
Related standards
- ISO 2469 - Measurement of diffuse radiance factor (diffuse reflectance factor)
- ISO 2470‑1 - Measurement for blue reflectance factor / ISO brightness (required for FWA adjustment)
- ISO 186, ISO 187 - Sampling and conditioning
- ISO 4094 - Competence of laboratories issuing optical reference standards
- ISO/CIE 11664 (Parts 1 & 2) and ASTM E308 - Colorimetry and illuminants
Keywords: EN ISO 12625-16:2024, tissue paper opacity testing, diffuse reflectance, paper backing, luminance factor, reflectometer, fluorescent whitening agents.
