ISO 12625-16:2024

Overview - ISO 12625-16:2024 (Tissue paper opacity, diffuse reflectance)

ISO 12625-16:2024 specifies an instrumental test method for determining the opacity of tissue paper and tissue products by the diffuse reflectance method with a paper backing. The standard defines how to measure the single-sheet luminance factor over a black cavity and the intrinsic luminance factor of an opaque pad, and then calculate opacity as their ratio. It covers single‑ply and multi‑ply preparations and accepts samples containing fluorescent whitening agents when the instrument UV content is adjusted to CIE illuminant C using an authorized fluorescent reference standard.

Key topics and technical requirements

• Principle: Opacity = (single-sheet luminance factor over black cavity) / (intrinsic luminance factor of an opaque pad).
• Apparatus:
  • Reflectometer calibrated and characterised per ISO 2469, with capability to measure luminance factor (C).
  • Options: filter reflectometer or abridged spectrophotometer able to compute CIE Y for illuminant C (Annex A provides weighting functions and bandpass correction guidance).
  • Black cavity with reflectance tolerance within 0.2%.
• Reference and working standards:
  • Non‑fluorescent photometric standard (ISO 2469).
  • Fluorescent reference standard to adjust UV content to UV(C) per ISO 2470-1.
• Sampling & conditioning:
  • Sampling per ISO 186 for lots; condition samples in standard atmosphere per ISO 187.
  • Remove first/last six layers from finished rolls to avoid adhesive/damage.
• Test pieces:
  • Minimum test-piece size: 50 mm × 50 mm or 50 mm diameter.
  • Prepare pads thick enough that doubling sheets does not change reflectance; compress and protect pads.
• Procedure & reporting:
  • Verify UV setting using authorized fluorescent standard.
  • Measure luminance factors, calculate opacity percentage, and include specified data in the test report.
• Precision & annexes:
  • Annex B gives precision data; Annex A details spectral characteristics and corrections.

Applications and who uses it

• Quality control and acceptance testing in tissue paper manufacturing.
• Laboratory test methods for R&D, supplier evaluation, and product specification compliance.
• Instrument manufacturers and calibration labs implementing reflectometers for tissue testing.
• Procurement, regulatory, and conformity assessment teams requiring standardized, comparable opacity data. Practical benefits: repeatable opacity measurements, accurate comparison across batches and suppliers, and meaningful assessment of visual hiding power (e.g., how a sheet obscures print on underlying sheets).

Related standards (for implementation)

• ISO 2469 - reflectometer characteristics and calibration
• ISO 2470-1 - fluorescent reference standard (UV(C) adjustment)
• ISO 186 - sampling to determine average quality
• ISO 187 - standard atmosphere for conditioning and testing
• ISO 4094 - competence of laboratories issuing optical reference transfer standards
• ISO/CIE 11664-1 / 11664-2 - colorimetry and standard illuminants

Keywords: ISO 12625-16:2024, tissue paper opacity, diffuse reflectance, reflectometer, CIE illuminant C, fluorescent whitening agents, luminance factor, paper backing, opacity test method.